Preheat oven to 300 degrees F (150 degrees C). Grease a cookie sheet.
In a large mixing bowl combine white flour, whole wheat flour, cracked wheat, cornmeal, garlic powder, brewer's yeast and instant milk. Stir in 2 cups broth. Mix the ingredients well using either your hands or an heavy duty electric mixer. The dough should be very stiff. Gradually mix in the remaining 1 cup broth to make a bread-dough consistency.
Roll the dough out to a 1/4 inch to 1/2 inch thickness on a floured board. Cut out biscuits into any shape you please. Place the biscuits on the prepared cookie sheet. Brush the tops of the biscuits lightly with milk.
Bake the cookies 45 minutes; turn oven off completely but do not remove the biscuits. Let the biscuits sit in the oven overnight (for 10 hours). Store biscuits in an air-tight container.
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