Combine the flour, baking powder, and baking soda into a large mixing bowl and whisk to combine. Make a well in the center.
In a large measuing cup, whisk the eggs and buggermilk.
Pour the eggs and buttermilk mixture into the well of the dry ingredients.
Using your hands, or a wooden spoon, combine the wet and dry ingredients until a ball forms.
Cover the bowl with plastic wrap and put into the refrigerator for 30 minutes or overnight.
Preheat over to 400 degrees F.
Turn the dough out onto a well-floured surface and flatten with your hand into a large round about a half-inch thick.
Using a 2 3/4 inch biscuit cutter, cut out as many biscuits as you can. Reform the scraps and repeat until all the dough is cut.
Put the biscuits on a parchment lined baking sheet. Make sure the biscuits are touching either other.
Whisk one egg with one tablespoon of buttermilk. Using a pastry brush, brush the mixture over the tops of the biscuits.
Bake for 15-20 minutes.