Preheat oven to 425°F. While oven is preheating add lemon juice to oat milk and let sit for 5 minutes.
In a large chilled mixing bowl, combine flour, rosemary, baking powder, baking soda and salt. Add the cold butter and combine, using a pastry cutter, until the pieces of butter are pea-sized or smaller. Add the oat milk mixture and combine until a sticky dough forms (don't overmix). Transfer to a lightly floured surface and fold the dough over itself 5 times. Using a pastry cutter or water glass, cut out the biscuits and transfer to a parchment-lined cookie sheet.
Bake for 10 to 15 minutes until the biscuits are starting to turn golden brown.