Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.

Whisk together self-rising flour and baking soda in a large bowl until well combined.

Cut the cold butter into small cubes and work it into the flour mixture until it resembles coarse crumbs.

Create a well in the dry mix, pour in buttermilk, and gently stir until just combined.

Transfer dough to a floured surface, shape into a rectangle about 1 inch thick, fold into thirds, and roll to ½-inch thickness.

Sprinkle half of the cheese and onions over the dough, fold in half, roll out, and repeat with remaining cheese and onions.

Cut out approximately 12 biscuits, pressing straight down without twisting.

Place cut biscuits on prepared baking sheet and brush tops lightly with buttermilk.

Bake for 20 minutes or until golden brown. Cool on a wire rack.