These biscuits are the perfect balance of buttery, sweet, and savory, resulting in a golden, fluffy addition to any meal. The true mark of perfect biscuits is the many layers, which involves multiple rounds of rolling and folding. When you taste these biscuits, you'll agree they're worth the effort.
Chill all the ingredients (except for the buttermilk) and all the equipment in the freezer, including the blade and bowl of the food processor. Combine the flour, baking powder, baking soda, kosher salt, and butter in the bowl of the food processor. Pulse the mixture until it is the texture of fine meal.
Transfer the flour mixture to a large mixing bowl. Make a well in the center, pour the buttermilk into the well, and mix by hand until the dough comes together.
Turn the dough onto a clean work surface, dust with flour, and roll it into a ½-inch thick rectangle, applying even pressure and squaring off the edges. Laminate the dough by folding it into thirds, like a letter, and dust with flour; then roll the dough into a ½-inch thick rectangle again. Repeat this procedure a total of seven times, dusting with flour as necessary.
Use the dough scraper to cut the dough into 2x2-inch squares; discard the excess dough. Place the cut biscuits on a baking sheet close together, with about ¼-inch or less between them, so they'll touch gently when they bake. Chill the cut biscuits for an hour.
Preheat the oven to 425 degrees F. Brush the tops of the biscuits with melted butter and sprinkle them with the sea salt. Bake the biscuits until they are golden brown, about 20 minutes. Remove them from the oven and serve warm.