6 tablespoons salted butter, melted
1/3 cup 2% milk
1 egg yolk
1 teaspoon vanilla
2 teaspoons lemon zest
1 1/2 cup flour
3/4 cup sugar
1 1/2 teaspoons baking powder
2 cups blueberries
Preheat oven to 375.
Melt butter in covered medium-sized bowl in microwave (about 20-30 seconds). Whisk in milk, vanilla, egg, yolk and zest.
In large bowl, whisk together flour, sugar and baking powder. Mix wet mixture into flour until just incorporated.
Carefully fold blueberries into muffin batter.
Line muffin tin with 12 liners. Divide batter evenly between liners. Bake oven on the middle rack for about 18-20 minutes, or until muffins are beginning to turn golden and an inserted toothpick comes out clean (no sticky dough).