Preheat the oven to 450 degrees F.
Grease the skillet with butter and set aside.
To a large bowl, add the flour, baking powder, salt, milk, sugar, and chilled small cubes of butter. With a pastry cutter or a large sturdy fork, cut the butter into the ingredients. Continue to mix the ingredients together with a fork until dough forms.
Sprinkle a light coating of flour on to a large cutting board and add the dough. Knead the dough a few times until the texture becomes sturdy enough to roll. Add a light coating of flour to a rolling pin and roll out the dough until it’s about 1-1/4 inches thick.
Using a 3-inch wide biscuit or cookie cutter, cut the dough into 2 large biscuits. Then re-roll the remaining dough and cut into 2 more large biscuits. Lay each biscuit in the greased skillet so that each biscuit is leaning against one another.
For the egg wash - (this is used to add color and shine to the top of the biscuits; since the biscuits will be topped with gravy, using an egg wash is optional). In a small bowl, add egg and cold water. Whisk together. Brush the top of each biscuit with an even coat of egg wash.
Bake in a preheated oven until the biscuits turn a light golden color (about 16 minutes). Remove the biscuits from the oven and serve while warm, topped with sage sausage gravy.