1. Preheat your oven to 350°F or 175°C. Line a 12-cup muffin tin with paper liners to make removal easier.

2. In a medium-sized bowl, whisk together the flour, baking powder, and salt until well combined. Set this mixture aside for now.

3. In a large bowl, use an electric mixer to cream together the butter and granulated sugar until the mixture becomes light and fluffy. Beat in the eggs one at a time, making sure each egg is fully incorporated before adding the next.

4. Add the flour mixture to the wet ingredients in three parts, alternating with the milk, beginning and ending with the flour mixture. Be gentle when combining these ingredients to avoid overmixing. Fold in the frozen blueberries.

5. Divide the batter evenly among the muffin cups, making sure not to overfill them. Create a small well in the center of each muffin and fill with a dollop of vanilla sugar.

6. Bake the muffins in the preheated oven for 20 minutes, or until they are golden brown. Remove the muffins from the oven and allow them to cool before dusting with confectioners sugar, if desired.