1Heat oven to 375°F for shiny aluminum pan, 350°F for dark nonstick pan. Place paper baking cup in each of 12 regular-size muffin cups, or grease cups with shortening or cooking spray.
2In medium bowl, stir together flour blend, poppy seed, baking powder, baking soda, xanthan gum and salt; set aside.
3In large bowl, beat granulated sugar and softened butter on medium speed about 3 minutes or until light and fluffy. Add eggs, one at a time, beating on medium speed 1 minute after each addition. Beat in sour cream, lemon peel and 2 tablespoons lemon juice until smooth. Gradually beat or stir in dry mixture (dough will be thick). Divide batter evenly among muffin cups. Smooth tops of batter in cups with wet fingers.
4Bake 20 to 24 minutes or until toothpick inserted in center of muffin comes out clean. Cool 5 minutes in pan; remove from pan to cooling rack. Meanwhile, in small bowl, mix powdered sugar and lemon juice until thin enough to drizzle. Drizzle over muffins.