Whisk flour, baking soda, salt, pepper, sugar and baking powder in a large bowl.
Using your fingers, work the butter pieces into dry ingredients, smashing and flattening to coat with flour, until you have some flat quarter-size pieces and some smaller pea-size pieces.
Add the green onions, rosemary and sage, tossing to thoroughly distribute. Add the buttermilk and stir mixture with a fork just until a shaggy dough forms. Turn dough out onto a lightly floured surface and knead once or twice gently to incorporate loose pieces.
Pat dough into a 10x8" rectangle. Cut dough in half crosswise and stack 1 piece on top of the other. Pat dough again into a 10x8" rectangle. Cut dough in half crosswise and stack 1 piece on top of the other (this process will build biscuit layers).
Pat dough into a 10x8" rectangle once more and cut into 12 even pieces. Place biscuits on a parchment-lined baking sheet, spacing evenly, and freeze 10 minutes.
Brush top of each biscuit lightly with buttermilk and bake, rotating biscuits halfway through, until golden brown, 24-26 minutes.