Preheat oven to 400°.
Place 12 muffin cup liners in muffin cups.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour and next 4 ingredients in a medium bowl; stir well with a whisk. Stir in lemon rind and poppy seeds; make a well in center of mixture. Combine buttermilk, butter, and egg; stir well with a whisk. Add to flour mixture, stirring just until moist.
Spoon batter into prepared muffin cups, filling 3/4 full. Bake at 400° for 20 to 22 minutes or until golden brown.
Cool in pan 5 minutes on a wire rack; remove from pan. Place on wire rack to cool completely.