Spray 12 regular-size muffin cups with cooking spray. In large bowl, beat eggs, melted butter and milk with whisk until well blended. Add flour, brown sugar, baking powder, sea salt and pepper; stir with spoon just until dry ingredients are moistened. Stir in sweet potatoes, kale and cheeses. Divide batter evenly among muffin cups, filling each about three-fourths full.