Whisk multi-grain flour, wheat flour, sunflower seeds, flax seeds, wheat germ, sugar, baking powder, and salt together in a large bowl.
Grate cold butter into flour mixture using the largest holes of a cheese grater and mix with a fork until it resembles coarse crumbs. Slowly pour in milk and mix until dough begins to pull away from sides of the bowl.
Turn dough out onto a lightly floured surface and gently knead to form a soft dough, about 10 turns. Pat into an 8-inch square, cut into quarters, and cut each quarter into 3 rectangular pieces.
Place each piece of dough onto an ungreased baking sheet, about 1 inch apart; brush with egg and sprinkle with sesame seeds.
Bake in the preheated oven until golden, 12 to 15 minutes.