Whisk first four ingredients in a large bowl. Place bread slices in a single layer in two 13x9x2” baking dishes. Pour custard over bread, dividing equally. Cover and refrigerate overnight. Preheat oven to 450 degrees. Butter 2 large rimmed baking sheets with some melted butter. Using spatula, transfer the bread slices to the prepared sheets. Brush bread with the remaining melted butter. Bake for 10 minutes and the turn the bread over and bake until golden about 6 minutes more. Remove from oven, place on a serving platter, and dust generously with powdered sugar.