Line two half sheet rimmed baking trays with parchment. Preheat oven to 200° C / 390° F.

In a large mixing bowl, stir together flour, 140 grams rolled oats, cream of tartar, baking soda, kosher salt, and black pepper.

Add the cubed butter to the bowl. With your hands, rub the butter into the flour until a coarse, sandy texture forms.

Add the buttermilk. With a bench scraper, work the buttermilk into the dry ingredients until a soft, shaggy dough forms.

Divide the dough into three equal portions** and place each in a separate bowl.

With your hands, knead the inclusions into each portion.

Divide each portion in half, and shape into balls. When finished, you should have 6 balls total.

Roll each ball in remaining oats, completely coating the surface of the dough.

Arrange 3 balls on each prepared tray.

With a serrated knife, kitchen scissors, or a bread lame, slice an “X” shape into the top of each ball of dough.

Bake in preheated oven for 30-35 minutes, rotating trays halfway through, until loaves are bubbly and golden brown.

Cool on a wire rack. Serve at room temperature or just slightly warm.