Cream butter and sugar together until light and fluffy. Add egg and mix well. Sift dry ingredients together. Add flour mixture to the butter mixture, alternating with milk. (Begin and end with flour for the best texture. Not sure why, but this works.) Toss blueberries with lemon rind and gently fold into batter. Do not over-mix.
Fill 12-cup muffin tin with paper cups or grease with butter. Fill 2/3 full with batter.
Bake in preheated 375F oven for 15-20 minutes. Remove from tins and cool on rack.