Preheat your oven to 375 degrees. Melt the butter and let cool slightly. Whisk in milk, egg, egg yolk, and vanilla until well blended.

In another bowl, whisk together the flour, sugar, baking powder, and salt.

Wash and pick over your blueberries.

Add the dry ingredients to the wet ones.

Mix until just combined. Fold in the blueberries.

In a small bowl, fork together the crumb topping ingredients (butter, flour, and sugar) until the mixture is crumbly.

Add the batter to muffin liners and sprinkle the top with the crumb mixture. Bake for 18 to 20 minutes or until a toothpick comes out clean.