Preheat oven to 425°F (220°C). Line 2 rimmed baking sheets with parchment paper.
In a large bowl, combine flour, sugar, baking powder, garlic powder, salt, and baking soda; sift flour mixture. Using a pastry blender or 2 forks, cut in cold butter until butter pieces are pea-size. Stir in cheese and green onion until well combined. Stir in cold buttermilk just until combined. (Dough may look dry and crumbly in spots but will come together later.)
Turn out dough onto a lightly floured surface. Gently knead 5 times. Pat dough into an 8-inch square, and cut into fourths. Stack each fourth on top of each other, and roll or pat down into an 8-inch square again. Repeat procedure twice. Roll or pat dough to 1-inch thickness. Using a 2¼-inch round cutter, cut dough without twisting cutter, rerolling scraps as needed. Place biscuits at least 1½ inches apart on prepared pans. Freeze for 15 minutes.
Brush egg white onto biscuits.
Bake until golden brown, 15 to 18 minutes. Let cool for 15 minutes. Serve warm.
Recipe by Bake from Scratch at https://staging.bakefromscratch.com/cheddar-onion-biscuits/