Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking dish.
In a large mixing bowl, whisk together the flour, sugar, baking powder, and salt until well combined.
In another bowl, mix the milk, eggs, melted butter, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and stir until just combined. Do not overmix; a few lumps are okay.
Gently fold in the blueberries.
Pour the batter into the prepared baking dish and spread it evenly.
Bake in the preheated oven for 25-30 minutes, or until the top is golden brown and a toothpick inserted in the center comes out clean.
Allow the casserole to cool for a few minutes before slicing. Serve warm with maple syrup and a dusting of powdered sugar if desired.