4 tablespoons unsalted butter, melted, plus more for the dish
8 croissants, sliced 1 inch thick (about 12 cups)
3 large eggs plus 3 egg yolks
1 1/2 cups whole milk
1 cup heavy cream
1/4 cup sugar
1 teaspoon pure vanilla extract
Pinch of salt
6 ounces milk chocolate, cut into 3/4-inch pieces
For the sauce:
cup heavy cream
2 tablespoons unsalted butter
2 tablespoons sugar
2 tablespoons light corn syrup
4 ounces bittersweet chocolate, chopped