Step 1 In a large bowl, whisk together the flour, sugar, baking powder and soda, salt and nutmeg. Transfer the mixture to the bowl of a stand mixer fitted with the paddle attachment (alternatively, the mixture can be mixed by hand). Scatter in the chilled butter pieces and beat until the butter is almost fully incorporated. Scrape down the bowl and add the bacon and grated Gruyère and cheddar cheese. On low speed, slowly add the buttermilk and beat until the mixture is just combined, careful not to overwork the dough.
Step 2 Turn the dough out onto a floured surface and press or roll to a thickness of approximately three-fourths of an inch. Fold the dough into thirds and repeat. Gently press or roll the dough into a rectangle shape measuring 8 inches by 6 inches. Cut the rectangle into 12 (2-inch) square biscuits.
Step 3Carefully transfer the biscuits to a rimmed baking sheet, spacing them an inch or so apart
Step 4Place the biscuits on the baking sheet in the freezer to chill for about 20 minutes. Meanwhile, heat the oven to 375 degrees.
Step 5Place the biscuits in the oven and reduce the heat to 350 degrees. Bake for 20 minutes, then rotate the baking sheet and continue baking until the biscuits are set and a light golden color, an additional 15 to 20 minutes.