Preheat the oven to 400°F. Line a baking sheet with parchment paper.
Combine self rising flour, salt, green onion, cheddar, and sour cream in a large mixing bowl.
Using a box grater, grate the cold butter into the flour. Toss to evenly coat the butter in flour while ensuring there are no large clumps.
Pour the cold milk over the flour mixture and stir to evenly combine. Stir until a shaggy dough is formed.
Empty the dough onto a lightly floured cutting board. With your hands, press the dough together until it starts to come together. Gently roll out the dough into a rectangle that's roughly 1 inch thick.
Working from the short side, fold one half of the dough on top of itself. Gently press the dough together. Gently roll the dough into another rectangle that is 2 inches thick. Wrap the dough in wax paper and chill in the freezer for 15 minutes.
Remove the dough from the freezer. Using a knife or pastry cutter, cut the dough into 8 even rectangles. Place them on the baking sheet 2 inches apart. Bake for 15 to 20 minutes until golden brown.