Preheat your oven to 400°F. Place a 10-inch oven-safe skillet over medium-high heat. Add the olive oil and let it shimmer.

Add the ground beef to the hot skillet. Break it apart with a wooden spoon and cook until browned, about 5 minutes. Stir in the diced onion and minced garlic. Cook for another 2 minutes until the onion is soft and translucent.

Reduce heat to medium. Stir in the salt, pepper, Worcestershire sauce, tomato paste, ketchup, and mustard. Let it cook for 1 minute, stirring constantly, until everything is well combined and fragrant. The sauce will thicken slightly.

Sprinkle the shredded cheddar evenly over the beef mixture. Remove the skillet from heat. The cheese will start to melt from the residual warmth.

In a medium bowl, whisk together the flour, baking powder, and baking soda. Cut in the cold butter using a pastry cutter or your fingertips until the mixture resembles coarse crumbs. In a small bowl, whisk the buttermilk and egg together. Pour the wet ingredients into the dry and stir just until combined. Do not overmix, a few lumps are fine.

Drop spoonfuls of the biscuit dough over the cheese-topped beef. It does not need to be perfect; a rustic look is part of the charm. Place the skillet in the preheated oven and bake for 18 to 22 minutes, until the topping is golden brown and a toothpick inserted into the biscuit comes out clean. The cheese will be bubbly around the edges.

Let the pie cool for 5 minutes before slicing. This resting time allows the layers to set. Serve warm, scooped directly from the skillet.