Preheat oven to 375°. Spray 2 (12-cup) muffin pans with cooking spray.

In a large bowl, whisk together flour, cornmeal, sugar, baking powder, salt, and garlic powder. Whisk in corn, eggs, and buttermilk. Fold in rosemary. Using a 3-tablespoon scoop, drop batter into prepared muffin cups.

Bake until a wooden pick inserted in center comes out clean, about 12 minutes. Let cool in pans for 10 minutes. Remove from pans, and let cool completely on wire racks.