Whisk 2 cups flour, 1½ tsp. baking powder, ¼ tsp. baking soda, 4 tsp. sugar, and 1½ tsp. salt in a large bowl to combine.

Finely grate zest of about half of 1 lemon right into bowl (reserve lemon for later).

Cut 1 stick cold butter into ½" pieces and toss with dry ingredients until coated. Work butter into dry ingredients by pinching and rubbing it between your palms until there are lots of flat shards and pea-sized bits remaining. Those small, uneven pieces of unincorporated butter create steam pockets as the shortcakes bake, resulting in a tender, flaky end result.

Combine ¾ cup sour cream and ⅓ cup heavy cream in a medium bowl. Create a well in the center of the dry ingredients. Scrape cream mixture into well. Working in circles from inside the well outwards with a rubber spatula, mix dough until large, shaggy clumps form.

Knead once or twice (don’t overdo it!) until it forms a mass and most of the flour has been incorporated into the dough.

Transfer to a lightly floured surface. Pat to a 1"-thick square (it should be about 6x6").

Cut dough into 4 equal squares, then stack them all on top of each other, creating one very tall tower of dough. Press down on stack with your hands, flattening dough back to a square. This stacking method is what will create lots of flaky layers. Pat to a 7½x5" rectangle about 1" thick.

Cut rectangle in half lengthwise, then cut each of those 2 rectangles into 3 squares.

Sprinkle tops with 1 Tbsp. sugar.

Transfer to a tray or plate, cover and refrigerate.