Preheat the oven and pan: Preheat oven to 400°F (220°C). Place a 9x13-inch baking dish in the oven with 2 tablespoons melted butter to melt while the oven comes to temperature. A hot, buttered pan is what creates the crispy golden edges.
Mix the batter: In a large bowl, whisk together 6 large eggs, 2 cups milk, 0.3 cups maple syrup, 1 teaspoons vanilla extract, and 0.5 teaspoons salt until smooth and fully combined. Gradually add 1 cups flour of choice, whisking as you go, until no lumps remain. The batter will be quite thin — that's exactly right.
Butter the pan and pour: Carefully remove the hot baking dish from the oven using good oven mitts. Swirl the melted butter to coat the entire bottom and sides. Immediately pour in the batter and return to the oven.
Bake: Bake for 20–22 minutes he pancake will puff up dramatically with golden, crispy edges and a custardy center. Resist opening the oven door early.
Cool, top, and serve: Let the pancake cool in the pan for a few minutes. It will deflate as it cools, which is completely normal. Top generously with 2 cups fresh mixed berries and an extra drizzle of maple syrup. Slice into squares and serve straight from the pan.
