In a medium bowl, stir together the flour, oats and flaxseed. Mix in 1/2 cup beef broth and peanut butter. Mix well, adding additional beef broth if necessary to bring the mixture together to a thick dough. Form into a ball and turn out on a lightly floured surface. Roll to about 1/4 inch thickness and cut out to desired shape. Bake for about 20 minutes or until golden brown, flipping halfway. Cool completely, then keep in an airtight container for about one week.