Preheat your oven to 400 degrees.

.Place the butter in a skillet in the oven until entirely melted – this usually takes between 1 and 2 minutes. Tilt the skillet, so the butter covers the entirety of it.

Spread the blueberries into the bottom of the skillet

Combine the eggs, flour, milk, sugar, vanilla extract, and cinnamon in a bowl and pour the mixture over the blueberries. Bake until the edges turn brown and the center is puffed. This takes around 30 to 35 minutes.