Preheat oven to 425°F (220°C). Slice ciabatta rolls in half horizontally. Brush cut sides lightly with olive oil and place cut-side up on a baking sheet. Toast in the oven for 5-7 minutes until edges are crisp and interior is lightly browned.

Season roast beef

While rolls toast, place thinly sliced roast beef in a bowl. Sprinkle with garlic powder and freshly ground black pepper. Toss gently to distribute seasonings.

Butter and assemble

Melt 2 tbs butter in a small skillet over medium heat. Lightly brush the toasted cut sides of the ciabatta with melted butter. Spread about 1/2 tbs mustard on the bottom half of each roll. Pile approximately 4 oz (about 1/4 lb) seasoned roast beef onto the bottom half of each roll (divide evenly across 4 rolls). Top the hot roast beef with two slices of provolone cheese each.

Melt cheese

Place assembled bottoms (meat + cheese) on the baking sheet and return to the oven for 3-5 minutes, or until cheese has melted and begins to bubble. Alternatively, cover briefly with a lid in the skillet to steam-melt the cheese. Top with the toasted roll halves and press gently.

Finish

Slice sandwiches in half if desired and set on a platter. Keep warm while you finish the au jus. Reserve any extra roast beef to add to the sandwiches or the au jus if desired.

Au Jus

Sauté aromatics

In a medium saucepan over medium heat, add 1 tbs butter. Once melted, add minced shallot and smashed garlic clove. Sauté 1-2 minutes until fragrant and softened but not browned.

Deglaze and build flavor

Add the optional red wine (1 tbs) to deglaze the pan, scraping any browned bits. Reduce slightly, about 30 seconds. Pour in 4 cups beef broth, then add Worcestershire sauce, soy sauce, beef drippings or au jus base, and thyme sprigs. Stir to combine.

Simmer

Bring the mixture to a gentle simmer. Reduce heat to low and let simmer uncovered for 8-10 minutes to concentrate flavor. Taste and adjust seasoning with salt and pepper.

Finish and strain

Remove thyme sprigs, garlic clove, and shallot. If you prefer a clearer jus, strain the liquid through a fine-mesh sieve into a bowl or saucepan. Stir in 1 tbs cold butter to add shine and roundness.

Optional thickening

If you prefer a slightly thicker jus, mix 1 tsp cornstarch with 1 tbs cold water to make a slurry. Whisk the slurry into the hot jus and simmer 1-2 minutes until slightly thickened. Remove from heat.

Serve

Ladle hot au jus into individual small bowls or one communal dipping bowl. Serve alongside the assembled French Dip sandwiches. Dip each bite of sandwich into the au jus as you eat.