Preheat the oven to 425 degrees.

Measure out 2 cups of flour and then remove a spoonful of it and mix it with your grated cheese.  Set floured cheese aside.

Add the baking powder and salt to the remaining flour in a medium mixing bowl. 

Cut your cold butter into 8-10 pieces, or use a large holed cheese grater to grate cheese directly into dry ingredients.

Combine the buttermilk and egg in a small measuring cup and beat lightly with a fork. Slowly drizzle into dry ingredients while lightly mixing with a fork. 

Add the cheese and gently combine.

Dump out onto a well-floured board and knead lightly lightly 3-4 times. 

Roll the dough out to a rectangle about 10 by 5 inches. With a sharp, floured knife, cut the dough lengthwise in half and then across in quarters, making 8 rough rectangles.  If preferred, cut to make 12 smaller biscuits.  Transfer to a sheet pan lined with parchment paper.

Brush the tops with the egg wash, and bake for 20 to 25 minutes, until the tops are golden brown and the biscuits are cooked through.  Serve hot or warm.