4 cups self-rising flour, plus more for dusting
2 tablespoons baking powder (see blog post above for more details; use double-acting, aluminum-free baking powder)
1 teaspoon baking soda
3/4 pound (3 sticks) SALTED butter, cold, cut into 1/2-inch cubes
2 large eggs, beaten PLUS 1 large egg for brushing
1 1/2 cups buttermilk, plus more as needed and for brushing
In a large bowl, whisk together flour, baking powder, and baking soda. Add the butter and using a pastry blender, cut the butter into the flour until pea-like crumbs form. Stir in the two beaten eggs with a wooden spoon until just combined. Then pour in the buttermilk until the dough comes together into a sticky mass. You may need more buttermilk if it's still too dry and there is flour still at the bottom of your bowl. I ended up having to add in 1/2 cup more. DO NOT add 1/2 cup more all at the same time. Do 1 tablespoon at a time until the right consistency is reached. Cover the bowl and refrigerate for at least 30 minutes.
When ready, preheat oven to 400 degrees Fahrenheit and line a baking sheet with parchment paper. Dust a little flour onto your work surface then put the dough onto the work surface and use your hands (flour them) to press into a round, roughly 14 inch diameter and 1/2 inch thick. See photos in the blog post.
Use a floured 2 3/4-inch round biscuit cutter to cut out about 20 biscuits. Reform the scraps of dough into a circle again to cut more.
Transfer biscuits to prepared baking sheet and arrange them so they are touching each other. See photos in the blog post. In a small dish, beat together remaining egg and 1 tablespoon of buttermilk then brush on top of the biscuits.
Bake for 15-20 minutes, or until the tops are golden brown.