Whisk 7 cups (875 g) all-purpose flour, ¼ cup (50 g) sugar, 2 Tbsp. plus 2 tsp. baking powder, 1 Tbsp. plus 1 tsp. garlic powder, 1 tsp. baking soda, 2 oz. Parmesan, finely grated (about 1 cup), ½ cup (packed) finely chopped parsley, 2 Tbsp. Diamond Crystal or 1 Tbsp. plus ½ tsp. Morton kosher salt in a large bowl to combine.

Add sliced 2 cups (4 sticks) chilled unsalted butter, thinly sliced; toss to coat, then smash into smaller, flatter pieces (about the size of a dime) with your hands.

Chill at least 15 minutes, or cover and chill up to 12 hours.

Drizzle 2½ cups buttermilk over butter mixture; toss with a fork to incorporate, then knead lightly in bowl until a shaggy dough forms (it will look dry).

Turn dough out onto a surface; pat into a 1"-thick square, gently pushing dry bits into dough as best as possible.

Roll slightly to flatten to about ½" thick.

Using a bench scraper, cut dough into 3 equal pieces.

Stack pieces on top of one another, sandwiching any loose dry bits of dough between layers; press down with your hands to flatten and pat into a rectangle.

Tidy edges with bench scraper.

Roll dough into a 1"-thick rectangle.

Repeat cutting, stacking, and rolling process 2 more times (dough will look less dry as you move to the final stage), making sure final rectangle is 1"–1¼" thick.

Wrap tightly in plastic and chill at least 1 hour and up to 12 hours.

Place a rack in middle of oven; preheat to 400°.

Unwrap dough and trim ⅛" off sides with a knife to tidy edges (this will also help biscuits rise later in the oven).

Cut dough into 4 equal rectangles, then cut each rectangle into 6 squares to make 24 biscuits total.

Arrange on a parchment-lined rimmed baking sheet, spacing about ¼" apart.

Chill 30 minutes, then bake until tops are golden brown, 35–40 minutes.

Just before the biscuits are finished baking, heat 4 garlic cloves, finely grated, a large pinch of salt, and remaining 4 Tbsp. (½ stick) unsalted butter in a small saucepan over medium until butter is melted.

Remove from heat and stir in remaining 3 Tbsp. finely chopped parsley.

Remove biscuits from oven. Brush garlic butter over; sprinkle lightly with Parmesan.