Preheat oven to 325°F. Spray a large casserole dish (9x13 inches or 2.5 quarts) with nonstick spray and set aside.
In a large mixing bowl, stir the melted butter and sugar together. Stir in the beaten eggs and milk.
4 tablespoons unsalted butter, 1½ cups granulated sugar, 3 large eggs, 1 cup milk
Add in the pineapple and remaining juice and stir to combine.
20 ounces pineapple tidbits
Fold in the bread cubes slowly, being careful not to crush the bread.
4 cups stale bread cubes
Pour the mixture into the prepared casserole dish.
Bake for 1 hour, or until the center is set.
Top with brown sugar or cinnamon sugar (optional).
Serve as a side dish or dessert.