Preheat your oven to 180°C and line a muffin tray with paper cups.
In a large bowl, whisk together the melted butter and sugar until smooth.
Add the eggs, one at a time, then mix in the yogurt and vanilla until everything is well combined.
Gently fold in the flour, baking powder, and salt using a spatula, just until combined.
Add the blueberries and give the batter a few gentle folds.
Scoop the mixture into the muffin cups and sprinkle brown sugar on top.
Bake for about 20 minutes, or until golden and slightly cracked on top.
