Combine the dry ingredients: flour, baking powder, baking soda, and salt in a large mixing bowl.

Before adding the chilled butter, cut it into 1/2-inch size pieces so it is easier to combine.

Add all the butter and use a pastry cutter* to combine the butter into the dry ingredients until the dough is crumbly and sandy with butter well-dispersed.

Add the wet ingredients: sourdough discard, buttermilk, and 50 grams (3 T.) water*. Mix into the dry dough with a rounded plastic dough scraper, stiff spatula, or large spoon.

Don't overmix, mix until nearly all the flour is hydrated. A little bit of dry flour is okay since you'll be shaping it soon which mixes in the remaining dry flour.

Shaping this dough into square biscuits is easier than using a biscuit cutter, creates less waste, and avoids overworking the dough.

Place the dough on a lightly floured surface. Lightly flour your rolling pin so it doesn't stick to the dough as you roll it out.

Roll out the dough until it is a 10-inch by 10-inch square with an even thickness (about 1 inch). Use the rolling pin to push in the edges to create a more square like shape and roll out high spots from the center out toward the corners.

Use a large knife or metal bench scraper to score the cutting lines before cutting. Divide the dough into 16 pieces by using the sharp edge to leave an indentation through the center of the square like a big cross or plus sign.

Then score each fourth through the center the same way to create 16 equally sized pieces.

Place cut biscuits 1-2 inches apart on a baking sheet lined with parchment paper. Cover with plastic wrap.

Place the covered biscuits into the fridge for at least 2 hours, up to 12 hours*. This is a great one to make ahead of time, place in the fridge and enjoy the next day!

Preheat the oven to 450 degrees F (232 degrees C).

Use a pastry brush to brush the extra buttermilk on the tops of the biscuits before they go into the oven. You can sprinkle on a pinch of flaked sea salt on each biscuit, if you'd like.

Bake for 13 to 15 minutes until the tops are golden brown and a toothpick inserted into the center comes out clean.

Let the biscuits cool for 5 to 10 minutes before serving.