Place the butter pieces evenly throughout a 9x13-inch baking dish.
Preheat the oven to 425°F (220°C). Place the baking dish in the oven while it preheats so the butter melts completely.
Add the milk, flour, eggs, maple syrup, vanilla, and salt to a blender.
Blend until the batter is completely smooth.
Carefully remove the hot baking dish from the oven.
Pour the batter directly over the melted butter. For extra puffiness, gently swirl the batter in a figure-eight motion as you pour.
Return the baking dish to the oven immediately.
Bake for 20 to 25 minutes, or until the edges are deeply puffed and golden brown.
Allow the pancake to cool for about 5 minutes before serving.