Place 1 1/2 sticks (12 tablespoons) of unsalted butter in the freezer for a minimum of 2 hours, or ideally overnight, until completely firm. Preheat the oven to 400ºF and set a rack in the center position. Line a baking sheet with parchment paper or a silicone baking mat for an easy cleanup and even baking.

In a large bowl, whisk together the all-purpose flour, baking powder, sugar, kosher salt, and baking soda. Grate the frozen butter directly into the flour mixture using the large holes of a box grater, allowing the butter to fall evenly throughout the dry ingredients. When you reach the final bit of butter, dice it finely and mix it in.

Use a fork to gently combine the grated butter with the flour, breaking up any clumps. Slowly pour in the buttermilk while gently tossing with the fork, just until a loose, shaggy dough begins to form. Using your hands, knead the dough a few times until it just comes together. Transfer to a lightly floured surface and shape into a rough 6-inch square, about 1-inch thick, pressing any stray bits into place.

Cut the dough into four equal squares and stack them to create flaky layers. Gently press the stack down and roll it into a 5x7-inch rectangle. Trim the edges if desired, then cut the dough in half lengthwise and into thirds crosswise, yielding six square biscuits. Arrange them on the prepared baking sheet with at least 2 inches of space between each.

Place the tray in the freezer for 10 minutes to firm the butter. Meanwhile, melt the remaining 4 tablespoons of butter. Brush the tops of the biscuits lightly with some of the melted butter, reserving the rest for after baking. Bake for 20 to 25 minutes, or until the tops are golden and the bottoms are deeply browned.

If your sausage is in casing, remove it before cooking. In a large skillet over medium heat, crumble the sausage and cook until well-browned and fully cooked, about 8 to 11 minutes. Stir occasionally, breaking it into small pieces with a wooden spoon.

Once browned, sprinkle the flour over the sausage and stir constantly for about a minute until the flour is absorbed and fragrant. Gradually pour in the milk while whisking continuously to create a smooth sauce. Cook the mixture, stirring often, until thickened and bubbling, about 3 minutes. Remove from heat and thin the gravy with a bit more milk if needed. Season with black pepper and salt, adjusting to taste. Keep covered and warm.

Brush the freshly baked biscuits with the remaining melted butter. Serve warm with a generous spoonful of sausage gravy over each biscuit. Add a dash of hot sauce for a spicy kick, if desired.