Black and White Croissant Bread Pudding

Name: Black and White Croissant Bread Pudding
Ingredients: 1 tablespoon unsalted butter, at room temperature; 3 medium eggs, plus 3 additional yolks; 1 cup heavy cream; 1 cup whole milk; 1/2 cup plus 1 tablespoon light brown sugar; 2 teaspoons vanilla extract; 5 one-day-old croissants; 5 ounces bittersweet chocolate chips (70% cacao); 5 ounces white chocolate chips; 1 cup crème fraîche or whipped cream