Preheat oven to 375°F. Spray standard 12-cup muffin pan with cooking spray. In small bowl, whisk together flour, baking powder, salt and nutmeg.
2. In large bowl, cream butter and sugar thoroughly. Beat in eggs and vanilla, then milk and lemon zest. Stir in flour mixture until just combined. Before adding blueberries, put a scant tablespoon of plain batter in each of the 12 cups (this ensures easy release from the pan). Stir in blueberries.
3. Divide batter among 12 muffin cups; they will be full. Bake at 375 degrees for 30 minutes. Cool on wire rack for 10 minutes before turning muffins out of pan. Makes 12 muffins.