Step 1

Line rimmed baking sheet with parchment paper. Whisk flour, sugar, parsley, chives, baking powder, baking soda, minced sage, and table salt together in large bowl. Coat sticks of butter in flour mixture, then grate 7 tablespoons from each stick on large holes of box grater directly into flour mixture. Toss gently to combine. Set aside remaining 2 tablespoons butter.

Step 2

Using rubber spatula, gently fold buttermilk into flour mixture until just combined (dough will look dry). Transfer dough to liberally floured counter. Dust surface of dough with flour; using your floured hands, press dough into rough 7-inch square.

Step 3

Roll dough into 12 by 9-inch rectangle with short side parallel to counter edge. Starting at bottom of dough and using bench scraper or metal spatula, fold into thirds like business letter. Press top of dough firmly to seal folds. Using bench scraper, turn dough 90 degrees clockwise. Repeat rolling into 12 by 9-inch rectangle, folding into thirds, and turning clockwise 3 more times, for a total of 4 sets of folds, sprinkling with extra flour as needed.

Step 4

Roll out dough into 12 by 9-inch rectangle, then sprinkle with Gruyère, leaving bottom 4 inches and ½-inch border around top and sides clear of cheese. Using bench scraper, fold cheese-free bottom third of dough up over center, then fold center up over top, tucking any cheese that may have escaped back underneath top fold. Press to seal, then roll dough into 8½-inch square, about 1 inch thick. Transfer dough to prepared sheet, cover with plastic wrap, and refrigerate for 30 minutes. Adjust oven rack to upper-middle position and heat oven to 400 degrees.

Step 5

Transfer dough to lightly floured cutting board. Using sharp, floured chef's knife, trim ¼ inch of dough from each side of square; discard. Cut remaining dough into 9 squares, flouring knife after each cut. Arrange biscuits at least 1 inch apart on now-empty sheet and place 1 sage leaf on top of each biscuit. Melt reserved 2 tablespoons butter, then brush sage leaves and tops of biscuits with melted butter.

Step 6

Bake until tops are golden brown, 22 to 25 minutes, rotating sheet halfway through baking. Transfer biscuits to wire rack, sprinkle with sea salt, and let cool for 15 minutes before serving.