FOR THE MUFFINS. In a medium bowl, combine flour, bran, brown sugar, baking powder, and salt. In a small bowl, whisk milk, oil, eggs, and maple extract. Make a well in center of dry ingredients and add milk mixture; stir just until moistened. Spoon about 2 Tablespoons batter into each cup of a greased muffin pan. Spoon about 2 teaspoons peanut butter mixture over batter in each cup. Spoon remaining batter over peanut butter mixture, filling each cup three fourths full. Bake 15 to 18 minutes or until muffins pull away from sides of pan. Remove from pan and cool completely on a wire rack. Store in an airtight container. Muffins may be served at room temperature or reheated.