Preheat the oven to 450 degrees F.
In a large bowl whisk together the flour, baking powder, baking soda, sugar and salt.
Pour in the buttermilk and melted butter and stir until a dough form. After the dough comes together give it a couple extra stirs just to make sure enough gluten has developed to give the biscuit structure.
Using a 3 ounce full portion scoop, dollop the dough onto a cookie sheet lined with parchment.
Combine the egg with 1 tablespoon water and whisk. Gently brush the tops of the biscuits.
Bake until the tops are golden and the center is just set, about 11-13 minutes.
Remove from the oven and enjoy immediately.
