Preheat the 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, garlic powder, and onion powder.
Add the cold, cubed butter to the flour mixture and use a pastry cutter or your fingers to mix until the mixture resembles coarse crumbs.
Stir in the shredded cheddar cheese.
Pour in the buttermilk and mix until just combined. Do not overmix.
Turn the dough out onto a floured surface and gently knead it a few times until it comes together.
Roll out the dough to about 1-inch thickness and cut out biscuits using a round cutter or a glass. Place them on the prepared baking sheet.
Bake the biscuits for 12-15 minutes or until golden brown.
While the biscuits are baking, prepare the dipping sauce by combining the beef broth, Worcestershire sauce, Dijon mustard, black pepper, and cayenne pepper in a small saucepan over medium heat. Bring to a simmer and keep warm.
Once the biscuits are done, remove them from the oven and let them cool slightly. Slice each biscuit in half and fill with sliced roast beef.
Serve the biscuits warm with the dipping sauce on the side, garnished with fresh parsley.