Step 1
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 giant bowl to combine. Add sliced 2 cups (4 sticks) chilled unsalted butter, thinly sliced; toss to coat, then smash into smaller, flatter objects (regarding the measurement of a dime) alongside along with your arms. Chill at least quarter-hour, or cowl and chill as a lot as 12 hours.
Step 2
Drizzle 2½ cups buttermilk over butter mixture; toss with a fork to incorporate, then knead evenly in bowl until a shaggy dough varieties (it’ll look dry). Flip dough out onto a flooring; pat proper right into a 1″-thick sq., gently pushing dry bits into dough as biggest as attainable. Roll barely to flatten to about ½” thick. Using a bench scraper, reduce dough into 3 equal objects. Stack objects on prime of one another, sandwiching any free dry bits of dough between layers; press down alongside along with your arms to flatten and pat proper right into a rectangle. Tidy edges with bench scraper. Roll dough proper right into a 1″-thick rectangle. (If dough is sticking to rolling pin, scrape off with bench scraper and press once more into greater block.) Repeat decreasing, stacking, and rolling course of two further cases (dough will look a lot much less dry as you progress to the last word stage), guaranteeing final rectangle is 1″–1¼” thick. Wrap tightly in plastic and chill at least 1 hour and as a lot as 12 hours.
Step 3
Place a rack in heart of oven; preheat to 425°. Unwrap dough and trim ⅛” off sides with a knife to tidy edges (this may occasionally additionally help biscuits rise later inside the oven). Decrease dough into 4 equal rectangles, then reduce each rectangle into 6 squares to make 24 biscuits full. Put together on a parchment-lined baking sheet, spacing about ¼” apart. Chill half-hour, then bake until tops are golden brown, 35–40 minutes.
Step 4
Merely sooner than the biscuits are accomplished baking, heat 4 garlic cloves, finely grated, a big pinch of salt, and remaining 4 Tbsp. (½ stick) unsalted butter in a small saucepan over medium until butter is melted. Take away from heat and stir in remaining 3 Tbsp. finely chopped parsley.
Step 5
Take away biscuits from oven. Brush garlic butter over; sprinkle evenly with Parmesan.