Preheat the oven to 450°.
In a large mixing bowl, whisk together dry ingredients.
Using a pastry cutter, cut butter into the dry mixture.
Add the egg, milk, and ½ cup buttermilk.
Mix until just combined.
Transfer the dough to a well floured surface, sprinkle additional flour on top of dough and knead 10-15 times.
Roll/pat dough out to 1 inch thickness and cut with a biscuit cutter.
Place biscuits on a lightly greased or non-stick baking sheet.
Brush tops of biscuits with remaining buttermilk and bake for 10-12 minutes or until the tops of biscuits are slightly brown.
Remove from oven and serve warm.