Preheat oven to 375 degrees and grease an 8X12 baking dish and set aside. In a large skillet heat 2 TBSP butter over medium high heat. Add the onion and cook, stirring until softened, but not browned, 3-5 minutes. Add the beef and cook, until no longer pink, about 5 minutes. Stir in tomatoes and beef broth, season with salt and pepper. Lower the heat and cook, stirring occasionally, until most of the liquid has cooked off, about 20 minutes, pour into the prepared baking dish.
In a large bowl combine the flour, baking powder, and 1/2 tsp salt. Using your fingertips or pastry blender, blend in 4 TBSP butter and the cheese until the mixture resembles coarse crumbs. Pour in the milk and stir quickly with the fork to form a dry shaggy dough. Gather the dough together and knead lightly in the bowl. Transfer to a floured work surface and roll or pat into a large 1/2 inch thick round. Using 3 inch cookie cutter cut out 8 biscuits. Gather scraps of dough and form into new round and cut out 1 more biscuit. Continue until all dough has been used.
Place biscuits on top of the beef mixture as close together as possible and bake until lightly browned, 35 minutes.