01 -
Preheat the oven to 425°F, or 400°F when using dark muffin pans. Generously grease 12 standard muffin cups.
02 -
In a large mixing bowl, blend together the flour, sugar, salt, baking powder, and dried rosemary until evenly combined.
03 -
Stir in shredded mozzarella, grated Parmesan, minced onion, and crushed garlic until distributed throughout the flour mixture.
04 -
In a separate bowl, thoroughly whisk the beaten egg with melted butter, then add milk and continue whisking until uniform.
05 -
Form a well in the center of the dry ingredients and pour the wet mixture into it. Gently fold together with a spatula, mixing just until the batter is moistened and lumpy—approximately 12 to 15 strokes. Do not overmix.
06 -
Spoon batter into muffin cups, filling each about two-thirds full to allow for expansion during baking.
07 -
Bake for 25 minutes, or until the muffins are golden brown and a tester inserted into the center comes out clean. Cool in the tin for 5 minutes before transferring to a wire rack.