Preheat your oven to 425°F (220°C) and line a baking sheet with parchment paper.
In a large bowl, whisk together the flour, baking powder, salt, and garlic powder.
Add the cold, cubed butter to the flour mixture. Use a pastry cutter or your fingers to mix until the mixture resembles coarse crumbs.
Pour in the buttermilk and stir until just combined. Do not overmix.
Turn the dough out onto a floured surface and gently knead it a few times. Pat it into a rectangle about 1 inch thick.
Cut the dough into 12 squares and place them on the prepared baking sheet.
In a separate bowl, mix the roast beef, provolone cheese, beef broth, Worcestershire sauce, thyme, and black pepper until well combined.
Spoon the beef mixture onto the center of each biscuit square. Fold the corners of the biscuit over the filling and pinch to seal.
Bake in the preheated oven for 15-20 minutes or until the biscuits are golden brown.
Serve warm with additional beef broth for dipping.