- Preheat and Prepare: Preheat your oven to 450°F (230°C). Place the stick of butter in your 9x13 inch baking dish and put it in the oven while it preheats to melt the butter completely. 
- Mix Dry Ingredients: In a large mixing bowl, whisk together flour, sugar, baking powder, and salt until well combined. 
- Add Wet Ingredients: Pour the buttermilk into the dry ingredients and stir just until a shaggy dough forms. Don't overmix. 
- Fold in Ham and Cheese: Gently fold the diced ham, cheddar cheese, and mozzarella cheese into the dough until evenly distributed. 
- Transfer to Pan: Carefully remove the hot baking dish from the oven. The butter should be completely melted and bubbling. Drop spoonfuls of the dough evenly over the melted butter, creating 12 portions. 
- Bake: Return to the oven and bake for 20-25 minutes, or until the tops are golden brown and the biscuits have risen significantly. 
- Cool and Serve: Let cool for 5 minutes before serving. The biscuits will absorb some of the butter as they cool.