Firstly, mill the flour, I like to use soft white wheat for these.
Then add baking powder, sugar, and salt to the flour and mix to incorporate.
Pour the buttermilk into the dry ingredients, and stir to combine. Let this mixture sit for about 10-15 minutes to give the fresh milled flour time to absorb the liquid, and soften the bran. (I do this while the oven is preheating, and the butter is melting.)
Place the butter into a 8x8 baking dish, and place that into the oven during the preheat. Preheat the oven to 450*F.
Let the butter melt during the oven preheat, once the oven is preheated, and the biscuit batter has had time to rest, then pour the batter into the melted butter. Be careful the baking pan will be hot!
Gently spread the batter as evenly as possible in the pan.
Using a butter knife, cut the unbaked batter into 9 equal squares (Like a Tic-tac-toe board.) The butter will work it's way into the cuts in the dough.
Bake for 26-30 minutes, until the tops of the biscuits are golden brown.
After baking, allow the butter to absorb into the biscuits. (about 5-10 minutes.)
Then, slice and enjoy! I have listed some great ideas how to enjoy these in the post above.