Step 1

Preheat oven to 400 degrees F. Line rimmed baking sheet with parchment paper.

Step 2

In a mixing bowl, stir the flour, baking powder, baking soda, and salt together.

Step 3

Grate 7 tablespoons of butter on large holes of a grater directly into flour mixture, stopping after about every 2 tablespoons to toss. You want to distribute the butter throughout and not let it clump up, which is why it should be very cold or frozen to begin with.

Step 4

Add the 2 tablespoons of sugar and stir until evenly blended.

Step 5

Add vanilla (or a different extract if you choose) to just a tablespoon of buttermilk and add to the flour mixture.

Step 6

Continue adding buttermilk to flour mixture 1 tablespoon at a time and stirring -- do it gradually rather than dumping it all in. Fold with a heavy duty scraper until dough is moist enough to hold together, but still looks kind of dry. Transfer dough to a pastry mat. If dough is very dry, don't add any flour to the mat yet.

Step 7

Press dough into a rectangle about 6 by 9 inches -- it doesn't have to be exact, just big enough so that you can easily fold it into thirds. If dough seems powdery on the mat and won't hold together, work in a little bit more milk. If it seems to wet, use more flour. Starting with short side, fold into thirds using bench scraper or metal spatula to pry from mat. Turn dough 90 degrees. Repeat rolling into rectangle, folding into thirds, and turning clockwise 2 more times. Press dough down again into a rectangle and stick frozen blueberries (or chocolate chips, nuts or add-ins you've chosen) in the dough. Fold again into thirds. Repeat one last time.

Step 8

Shape into a 6 inch circle that is a little over 1 inch thick. The dough circle should still be very cold. If for some reason it has gotten warm or butter has gotten really soft, throw the whole circle in the freezer for 10 minutes.

Step 9

Transfer dough to lightly floured cutting board. Using sharp, floured chef’s knife, cut into six triangles. Brush tops of dough with heavy cream. Alternatively, melted butter. Sprinkle generously with sparkling sugar.

Step 10

Bake at 400 until tops are golden brown, 18 to 20 minutes. Let cool for 15 minutes before serving.