# Classic Roast Beef Sandwich with Homemade Au Jus and Caramelized Onions > A hearty, savory roast beef sandwich topped with sweet caramelized onions and melted provolone, served with a rich homemade au jus for dipping. Perfect for turning leftover roast beef into an elevated snack or casual meal. Canonical URL: https://www.topshelf.recipes/recipes/classic-roast-beef-sandwich-with-au-jus-caramelized-onions ## Author Jake Woods https://www.topshelf.recipes/chef/jake-woods Published: June 25, 2026 Last Updated: September 25, 2026 ## About This Recipe This roast beef sandwich is built on a simple principle: treat each component with intention. Thinly sliced leftover roast beef is warmed gently in a flavorful au jus so it stays tender instead of drying out; sweet, slowly caramelized onions lend an almost jammy counterpoint and provolone provides a melty, slightly nutty blanket. Using sturdy sandwich rolls that are lightly toasted keeps the assembly from collapsing into sogginess while still letting you tear into warm, juicy layers with each dip into the au jus. What makes this version work is the orchestration of temperature and timing — onions cooked low and long, beef heated just enough to take the chill off in a savory bath, and cheese melted seconds before serving. The au jus is a small, punchy sauce (red wine and Worcestershire for depth) rather than a syrupy gravy, so it enhances without overpowering. This is a great weekend lunch or a way to elevate holiday roast leftovers into something celebratory yet relaxed; it’s equally at home beside a bowl of fries for casual company or plated with a crisp salad for a more composed meal. ## Recipe Information - Prep Time: 10 minutes - Cook Time: 35 minutes - Total Time: 45 minutes - Servings: 3 - Difficulty: Medium - Category: Snacks ## Ingredients ### Make the au jus and warm the beef - 12 oz Leftover roast beef, thinly sliced - 2 cups Beef broth (low-sodium preferred) - 1/4 cup Dry red wine (or additional beef broth) - 1 tbsp Worcestershire sauce ### Prepare and toast the rolls - 4 rolls Sandwich rolls (kaiser or French), split ### Caramelize the onions - 2 medium Yellow onions, thinly sliced - 2 tbsp Unsalted butter - 1 tbsp Olive oil ### Assemble and melt the sandwiches - 4 slices Provolone cheese slices ## Instructions ### 1. Caramelize the onions Heat butter and olive oil in a large skillet over medium-low heat. Add the thinly sliced onions and a pinch of salt, then cook gently, stirring every few minutes, until deep golden and sweet, about 25–30 minutes; adjust heat to prevent burning. ### 2. Make the au jus and warm the beef In a small saucepan, add red wine and simmer 1–2 minutes to reduce slightly, then add beef broth and Worcestershire sauce and simmer 5–7 minutes to marry the flavors. Add the sliced roast beef to the simmering au jus just to warm through (30–60 seconds) so it stays tender; keep the au jus hot for serving. ### 3. Prepare and toast the rolls Preheat broiler or oven to 375°F (190°C). Split the rolls and place cut-side up on a baking sheet; toast in the oven or under the broiler for 2–4 minutes until lightly golden. Remove and keep warm. ### 4. Assemble and melt the sandwiches Pile warmed roast beef on the bottom halves of toasted rolls, top with a generous spoonful of caramelized onions and a slice of provolone. Return sandwiches to the oven or place under the broiler for 1–2 minutes until the cheese melts and edges are bubbly. ### 5. Serve with au jus for dipping Transfer the au jus to small individual dipping bowls and serve alongside the assembled sandwiches so each person can dip as desired. Enjoy immediately while hot for the best texture and flavor. ## Nutrition Estimated nutrition per serving (1 serving): - Calories: 812 kcal - Protein: 54.6 g - Carbohydrates: 67.9 g - Fat: 33.2 g - Saturated Fat: 15 g - Fiber: 4 g - Sugar: 10.4 g - Cholesterol: 134.5 mg - Sodium: 1367.1 mg - Potassium: 979.9 mg - Calcium: 443.9 mg - Iron: 7.5 mg ## Tips ### Slice onions uniformly Cut onions into evenly thin slices so they caramelize at the same rate and you avoid burnt edges or raw centers. ### Low-and-slow caramelizing Cook onions on medium-low and resist frequent stirring; patience concentrates sugars and develops deep color without burning. ### Warm beef briefly Drop the roast beef into simmering au jus for only 30–60 seconds to warm through — any longer and thin slices will overcook and toughen. ### Toast rolls properly Toast cut-side up until just golden to create a moisture barrier; under the broiler, keep the pan a rack below the element to prevent scorching. ### Use pan juices if available If you have roast drippings, skim fat and add a spoonful to the au jus for extra depth and an authentic roast flavor. ## Variations and Substitutions ### French dip classic Use a long hoagie roll and swap provolone for thinly sliced Swiss; add a splash of soy sauce to the au jus for extra umami. ### Horseradish kick Stir prepared horseradish into softened butter and spread on the rolls before toasting for a bright, spicy edge that pairs beautifully with beef. ### Mushroom seitan substitute For a vegetarian take, replace beef with thinly sliced, well-seasoned seitan or sautéed cremini mushrooms and use vegetable broth in the au jus. ### Cheesy swap Switch provolone for aged Gruyère or sharp cheddar for a nuttier, more assertive melt that stands up to robust onions and au jus. ## Notes This sandwich shines when you want a comforting, restaurant-style bite from leftovers; the homemade au jus is the secret that turns simple ingredients into something special. It’s great for game day, quick dinners, or a weekend treat. ### Storage and Make-Ahead Store leftover components separately: au jus in an airtight container in the refrigerator for up to 3–4 days, caramelized onions for 4–5 days, and sliced roast beef for 2–3 days. Reheat beef gently in the au jus over low heat just until warmed to avoid drying; reheat assembled sandwiches in a 350°F oven wrapped loosely in foil for 8–10 minutes to melt cheese without making the roll soggy. ### Serving Suggestions Serve each sandwich with a small bowl of au jus for dipping and a scattering of extra caramelized onions on top. Crisp shoestring fries, a sharp vinegary coleslaw, or dill pickles cut the richness nicely, while an amber ale or a medium-bodied red like a Merlot complements the beef and caramelized sweetness. ## Frequently Asked Questions ### Can I use freshly roasted beef instead of leftovers? Yes — let the roast rest and slice it very thinly across the grain, then warm the slices briefly in the au jus; overcooking fresh slices will make them tough, so heat sparingly. ### How do I make the au jus richer without wine? Add a tablespoon of reduced balsamic or a teaspoon of tomato paste sautéed briefly, or use a splash of Worcestershire and a spoonful of pan drippings to deepen flavor without wine. ### My rolls got soggy — how do I prevent that? Toast the cut sides until golden to form a barrier and assemble just before serving; reserve some au jus for dipping rather than pouring inside the sandwich. ### Can I thicken the au jus into a gravy? Yes — whisk a cornstarch slurry (1 tsp cornstarch + 1 tbsp water) into simmering au jus and cook until slightly thickened, but keep it light if you want a true dipping jus. ### Is there a shortcut for caramelized onions? You can speed things up by adding a pinch of baking soda to the onions to accelerate browning, but use sparingly (a pinch) as it changes flavor; otherwise cook low and slow for the best result. ## Related Recipes and Guides - [Easy Peanut Butter Bars](https://www.topshelf.recipes/recipes/easy-peanut-butter-bars) - [Fried Jalapeno Rings](https://www.topshelf.recipes/recipes/fried-jalapeno-rings-lime-ranch) - [Gluten Free Fried Pickles](https://www.topshelf.recipes/recipes/gluten-free-fried-pickles) - [Labor Day Grilled Lobster Rolls with Charred Scallion Brown Butter & Lemon‑Herb Aioli](https://www.topshelf.recipes/recipes/labour-day-grilled-lobster-rolls-charred-scallion-brown-butter-lemon-herb-aioli) - [Salt & Vinegar Potato Chips](https://www.topshelf.recipes/recipes/salt-and-vinegar-potato-chips) - [Holiday Cranberry Maple Chex Mix](https://www.topshelf.recipes/recipes/holiday-cranberry-maple-chex-mix) - [Gluten-Free Weeknight Grilling Plan](https://www.topshelf.recipes/articles/gluten-free-weeknight-grilling-plan) - [Low-Fat Grill Swaps for Big Flavor](https://www.topshelf.recipes/articles/low-fat-grill-swaps-big-flavor) - [DIY Edible Monster Eyes Candy](https://www.topshelf.recipes/articles/diy-edible-monster-eyes-candy)