Created by Northwestgal on January 31, 2022
Step 1: Preheat oven to 350°F. Line a baking sheet with parchment paper (makes clean-up easier in case any of the cheese melts onto baking sheet).
Step 2: In a large skillet over medium-high heat, melt 2 tablespoons butter. Add onion and 2 thyme sprigs to the butter. Season with salt and pepper. Cook, stirring occasionally, until onions are caramelized (it should take 15 to 25 minutes). Discard thyme sprigs.
Step 3: Fold each slice of roast beef and each cheese slice in half, and then fold it in half again. It should be just about the size to fit on a slider bun.
Step 4: Place bottom half of each slider bun on a large baking sheet (cut side up). Top each bottom bun with a slice of roast beef, a slice of provolone cheese, and a good portion of caramelized onions. Top each slider with a bun top.
Step 5: Melt 2 tablespoons butter, and then brush the melted butter on each bun top. Then sprinkle garlic powder, coarse salt, and parsley on each bun top. (NOTE: If you're sensitive to salt or are on a low-sodium health plan, you can easily skip adding coarse salt to the bun tops in this step.)
Step 6: Place baking sheet in oven, and bake 10 to 15 minutes or until sliders are heated throughout and the cheese is melted and gooey.
Step 7: While sliders are baking, make Au Jus: Add remaining 1 tablespoon butter to the same skillet over medium heat. Add garlic and cook 1 minute or until fragrant. Add beef broth, Worcestershire, Better than Bouillon, and 1/4 tsp thyme to the skillet. Season with additional salt and pepper, if desired. Simmer 10 minutes or until slightly reduced.
Step 8: Serve sliders immediately with the hot Au Jus, for dipping.