French Dip Roast Beef Baguette with Rosemary Au Jus Step-by-step instructions

Before you start

Before starting, gather all your ingredients and equipment. Slice the onions and have the roast beef ready. Make sure you have a large skillet, a baking sheet, and a chef's knife.

If you are using a baguette that is very long, you may need to cut it into two or three pieces to fit on the baking sheet. Have the broth measured and the herbs ready to go. This recipe moves quickly once you start cooking, so being prepared will make the process smooth and enjoyable.

Instructions

Caramelize and Simmer

1. 1Caramelize the Onions
   In a large skillet, melt the butter over medium heat. Add the sliced onions and cook, stirring occasionally, until they are soft and deeply golden brown, about 10 minutes. This builds the sweet base for the sandwich.
   Look for Onions are browned, soft, and smell sweet.
   Tip Be patient; slow cooking prevents burning and brings out the natural sugars.
2. 2Simmer the Au Jus
   Pour the beef stock into the skillet with the onions. Add the Worcestershire sauce, rosemary sprig, and thyme sprig. Bring to a simmer and let it cook for 15 minutes to meld the flavors.
   Look for The liquid is steaming and smells richly herbal.
   Tip Keep the heat low enough to maintain a gentle simmer, not a rolling boil.
3. 3Warm the Beef in the Au Jus
   Using tongs, submerge the roast beef slices directly into the simmering au jus for about 30 seconds, until just heated through. Remove and set aside on a plate.
   Look for Beef is warmed and coated in the broth.
   Tip Do not leave the beef in too long or it will overcook and become tough.

The skillet is filled with golden, sweet onions and a fragrant, bubbling au jus. The aroma of butter, herbs, and beef broth fills the kitchen.

The onions have reduced and are glossy with butter. The au jus is a deep brown and smells rich and savory. The beef is warmed and glistening with broth.

Assemble and Broil

4. 4Assemble the Sandwiches
   Preheat the broiler. Place the baguette halves cut-side up on a baking sheet. Pile the warm roast beef evenly onto the bottom half, then top with the caramelized onions from the au jus. Lay the provolone slices over the top.
   Look for Sandwich is piled high and ready for melting.
   Tip Use the onions from the au jus for extra flavor.
5. 5Broil Until Bubbling
   Place the assembled baguette under the broiler for about 3 minutes, until the cheese is melted and bubbling and the bread edges are toasted and crisp.
   Look for Cheese is golden and bubbly, bread is crusty.
   Tip Watch closely to prevent burning; broilers vary in intensity.

The baguette is piled with rosy roast beef, caramelized onions, and slices of provolone. The top is golden and bubbly, with the cheese melted and slightly browned at the edges. The bread is crisp to the touch, and the whole sandwich looks irresistible.

Slice and Serve

6. 6Slice and Serve
   Remove the sandwich from the broiler. Using a sharp chef's knife, slice the baguette diagonally into individual portions. Serve hot with the remaining au jus on the side for dipping.
   Look for Sandwich is sliced into neat diagonal pieces.
   Tip Slice just before serving to keep the bread crisp.

The sandwich is sliced diagonally, revealing the layers of beef, onions, and melted cheese. The au jus is served alongside in small bowls for dipping. The first bite yields a satisfying crunch, followed by juicy, savory beef and the rich, herby broth.

Common mistakes

One common mistake is overcooking the roast beef in the au jus, which makes it dry and tough. Just a 30-second dunk is enough to warm it through. Another pitfall is not caramelizing the onions long enough; they need about 10 minutes to develop their sweetness and color.

Keep the heat at medium and stir occasionally to prevent burning. Also, be careful not to overfill the sandwich, as it can become unwieldy and fall apart when dipping. Finally, don't skip the broiling step – that crusty, toasted bread is essential for the perfect texture.

How to tell it’s done

The onions are done when they are soft and deeply caramelized, with a rich brown color and a sweet aroma. The au jus should be simmering gently and have a deep, savory flavor.

The beef is ready when it is heated through but still tender and pink in the center; it should not be gray or overcooked. The sandwich is done when the cheese is fully melted and bubbling, and the bread edges are golden brown and crisp. Serve immediately for the best texture.