Use 2 tablespoons of the melted butter to generously grease the bottom and sides of an 18-by-13-inch half-sheet pan.
Into a blender, add the eggs, milk and vanilla. Next add the flour, baking powder, sugar, salt and 4 tablespoons of the melted butter. Blend until just combined, about 30 seconds.
Pour the mixture into the prepared pan. Imagine the sheet pan in thirds, then sprinkle the chocolate chips in the first third, the blueberries in the second and the strawberries in the third, making 3 sections or stripes. Bake until golden brown and cooked through, about 20 minutes. Remove from the oven and brush with the remaining 2 tablespoons of melted butter.
To serve, cut a square of the chosen flavor of pancake and top with some warm maple syrup.