Butter Crackers

Preheat the oven to 400°F. Line 2 baking sheets with parchment and set aside.
Sift the white spelt flour, white whole-wheat flour, oat flour, baking powder, sugar, and salt together. Pour into the bowl of a food processor fitted with the dough blade (or in the bowl of a stand mixer fitted with the paddle attachment). Add the chilled butter and pulse to create a coarse crumb mixture. With the food processor running, stream in the flaxseed oil, followed by the water, 1 tablespoon at a time, until the mixture starts to form large clumps.
Turn the dough out onto a well-floured surface and gather it into a ball. Knead gently once or twice. Sprinkle a little more flour on top of the dough and roll it out until it is 1/4 inch thick, rotating the dough by 90 degrees after each roll.
Prick the dough all over with a fork, making sure it is well pierced. Using a small cookie cutter of your choice, cut out the crackers and carefully place them on the prepared baking sheets.
In a small bowl, lightly whisk the egg with the milk. Using a pastry brush, coat the tops of the crackers with the egg wash.
Bake just until the crackers begin to brown, 5 to 10 minutes.
While the crackers are baking, stir the melted butter and salt together in a small bowl. Brush the mixture onto the freshly baked, still warm crackers before serving.