Preheat oven to 400°F (200°C).

Prepare a 12-cup muffin tin by spraying with cooking spray or lining with paper liners.

In a large bowl, sift together the flour, sugar, baking powder, and baking soda.

Add salt and stir in the crushed rosemary.

Create a well in the center of the dry ingredients.

In a separate medium bowl, whisk together the melted butter, buttermilk, and grated onions until well combined.

Pour the wet ingredients into the well of the dry ingredients.

Stir gently until just moistened, being careful not to overmix.

Spoon the batter into the prepared muffin cups, filling each about two-thirds full.

Sprinkle the tops of the muffins with grated parmesan cheese.

Bake in the preheated oven for 15 minutes, or until the tops are golden brown and a toothpick inserted into the center comes out clean.

Remove the muffins from the oven and let them cool in the muffin tin for a few minutes.

Transfer the muffins to a wire rack to cool completely.

Serve warm.