Blend the cooked sweet potato with the buttermilk. Set Aside. (can alternatively whisk together by hand)
Whisk to combine the dry ingredients in a large bowl. Then, add sliced butter
Using a fork or pastry cutter, break down the butter into the flour until until the mixture resembles coarse meal with some pea-size chunks of butter within. Then, add the sweet potato puree
Using a rubber spatula, fold until the mixture is just moistened and holds together, adding up to 2 more tablespoons of milk if needed; do not overwork the dough. Gently knead it 3-4 times with your hands until it forms a smooth ball.
Flatten the dough into a rectangle about ¾ inch thick.
Cut it into three equal pieces, stack them on top of each other, and flatten again into a ¾-inch thick rectangle, adding a little flour if it starts to stick. Repeat this process twice, folding the dough onto itself and flattening gently into 3/4 inch triangle after each fold
Lightly coat a sharp knife with flour and cut the dough into 12 small squares. Place the squares on the prepared baking sheet and transfer to the fridge to chill for 15 minutes.
Bake at 400F for 24-26 minutes or until golden brown. Baking time depends on how thick you have rolled the dough. If your dough is thinner than ¾" inch please reduce the baking time to 21-23 minutes or until golden brown.