1¼ cups (284 grams) unsalted butter1 tablespoon (4 grams) packed fresh sage leaves3¾ cups (469 grams) all-purpose flour2 tablespoons (24 grams) granulated sugar1 tablespoon (15 grams) baking powder1 tablespoon (9 grams) kosher salt1 teaspoon (2 grams) garlic powder1/2 teaspoon (2.5 grams) baking soda1 cup (240 grams) cold whole buttermilk1 large egg, (50 grams), lightly beaten1 tablespoon (15 grams) waterFlaked sea salt , to tasteSoftened butter , to serve
In a light-colored medium saucepan, melt butter over medium-high heat. Add sage, and cook, stirring frequently, until milk solids at bottom have turned a deep amber color and butter is fragrant, 8 to 10 minutes. Pour into a shallow heatproof baking dish, and refrigerate until solid, at least 30 minutes.
Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper.
In the work bowl of a food processor, pulse flour, sugar, baking powder, kosher salt, garlic powder, and baking soda until combined. Add firm browned butter, and pulse just until butter resembles small peas and mixture is crumbly. Add cold buttermilk, and pulse until a shaggy dough forms.
Turn out dough onto a lightly floured surface. (Dough will be crumbly and almost dry.) Pat dough into a rectangle about 1 inch thick, and cut into fourths. Stack fourths on top of each other and pat down into a rectangle. Repeat procedure 3 times. Pat or roll dough to ¾-inch thickness. Using a 2/-inch round cutter dipped in flour, cut dough without twisting cutter, rerolling scraps as necessary. (To reroll scraps, stack pieces on top of each other, and pat to ¾-inch thickness.). Place 2 inches apart on prepared pan. Refrigerate until cold, about 10 minutes.
In a small bowl, whisk together egg and 1 tablespoon (15 grams) water. Brush biscuits with egg wash, and season with sea salt.
Bake until golden brown, 15 to 18 minutes. Serve warm with softened butter.