Buttermilk Biscuits

2 cups unbleached all-purpose flour, plus more for work surface

1 tablespoon baking powder 

1 teaspoon kosher salt 

1 tablespoon granulated sugar 

1/2 cup (1 stick) unsalted butter, frozen 

1 cup cold buttermilk 

1 large egg, beaten

Heat oven to 400°F. Line a baking sheet with parchment paper. 

In a large bowl, stir together flour, baking powder and salt. Using the largest holes on a cheese grater, grate the frozen butter into the flour and mix with a fork to coat the butter with the flour. Add the buttermilk; mix just until the mixture forms large clumps and starts to come together. Turn dough onto a lightly floured surface and roll into a 1-inch-thick rectangle. Cut into 8 squares and transfer to prepared baking sheet. Brush with beaten egg and transfer to the oven. 

Bake until golden brown and cooked through, 12 to 14 minutes. Serve warm.