Dough: Preheat oven to 425°. Stir the flours, fine salt, and rosemary together in a medium mixing bowl. Stir in the main part of the olive oil, then rub the mixture between your fingers to break up any lumps and work the crumbs into the texture of cornmeal. Stir in the milk and water to form a medium-stiff dough, add more water a tablespoon at a time.

Rolling: Line a large cookie sheet or back of a baking sheet with parchment paper. Roll the dough into a rectangle the size of the pan. Roll it up on the rolling pin and transfer to the parchment. With a pastry wheel, cut the dough into a 6x4 grid for 24 crackers. Brush tops with remaining olive oil, and sprinkle with sage leaves and kosher salt.

Baking: Bake the crackers until they are browned around the edges and in spots throughout, 16–18 minutes. Slide the crackers onto a wire rack. If the crackers in the middle of the pan seem softer and less done, return them to oven for 3–5 minutes. Cool the crackers for at least 30 minutes before serving to give them a chance to crisp. Store in an airtight container for up to one week.