Preheat oven to 350. Spray muffin tin with cooking spray and set aside. You can also line the tin with cupcake liners for easier cleanup.

Whisk the flour, baking powder and salt together in a bowl.

In a second bowl, whisk the egg and sugar until thick and combined. Just a few seconds should do it.

Add the melted butter to the egg and sugar in two additions mixing well between.

Add sour cream to the egg mixture in two additions, mixing well between.

Add the blueberries (still frozen) to the flour and toss with your hands to coat.

Add the sour cream/egg mixture to the flour and fold together with a rubber spatula.

This batter is very thick and some of your blueberries will break as you stir. Just be as gentle as you can and try not to turn it all purple.

Some small bits of flour may remain in the batter. Don't overmix it.

Spoon into muffin tins, filling 3/4 full. Bake 25 to 30 minutes or until a toothpick comes out mostly clean.

Optional: after they have cooled five minutes, melt a couple of tablespoons of butter and dip the tops in cinnamon sugar.