Preheat oven to 425°F (220°C). Line a baking sheet with parchment paper.

In a large bowl, whisk together flours, sugar, baking powder, baking soda (optional, for extra rise) and kosher salt. Using a pastry blender or 2 forks, cut in cold butter until mixture is crumbly. Stir in cold buttermilk until a shaggy dough forms.

Turn out dough onto a lightly floured surface. Pat dough into a rectangle, and cut into fourths. Stack each fourth on top of each other, and pat down into a rectangle. Repeat procedure 3 times. Pat or roll dough to 1-inch thickness. Using a 2½-inch round cutter dipped in flour, cut dough without twisting cutter, rerolling scraps as necessary.

Place biscuits 2 inches apart on the prepared pan. Freeze until cold and firm, about 40 minutes to 1 hour, or overnight.

Brush biscuits with egg, and sprinkle with sea salt.

Bake until golden brown, about 15 to 20 minutes, depending on how frozen biscuits were.

Serve warm with softened butter and honey. Store leftovers at room temperature in an airtight container for up to 2 days.