How to Make It
Preheat oven to 475°F. Stir together flour, cheese, chives, baking powder, pepper, salt, garlic powder, and baking soda in a large bowl. Whisk together buttermilk and mustard in a small bowl. Grate frozen butter into flour mixture using the large holes of a box grater; stir until well coated. Add buttermilk mixture; stir until just combined.
Drop batter in 2 1⁄2- to 3-tablespoonful rounds onto 2 baking sheets lined with parchment paper, leaving 3 inches between rounds.
Bake in preheated oven until biscuits are golden brown, 14 to 18 minutes, rotating baking sheets between top and bottom racks halfway through baking time. Brush biscuits with melted butter; garnish with sliced chives. Serve warm.