Preheat oven to 375 degrees. Lightly coat a standard 12-cup muffin tin with cooking spray. Whisk together flour, cornmeal, sugar, baking powder, baking soda, salt, rosemary, and 1 cup corn.
Combine buttermilk, egg, and oil in a small bowl. Add to flour mixture, and stir until just combined.
Spoon batter into muffin cups, filling three-quarters full. Top with remaining 2 tablespoons corn and the rosemary. Bake until tops are golden and a toothpick inserted into centers comes out clean, 15 to 17 minutes. Let cool in tin on a wire rack for 5 minutes. Turn out muffins onto rack. Serve warm or at room temperature. Muffins can be stored in an airtight container for up to 2 days.