If your bread is not already slightly hard or stale, prepare it by either letting the slices sit uncovered for a day, or arranging them on a baking sheet and baking at 300°F (150°C) for 15 minutes until dried out. This helps the bread soak up the custard later without becoming mushy.

Grease a 9x13 inch baking pan to prevent sticking. Cut the dried bread into approximately 1-inch pieces and arrange them evenly in the prepared pan.

In a large bowl, whisk together the applesauce or mashed banana, milk, liquid egg whites (or extra milk), maple syrup (or agave/honey), and vanilla extract (if using). Whisk until thoroughly blended. I prefer to use real vanilla extract here—it adds a nice aroma to the casserole.

Pour the prepared custard mixture evenly over the bread pieces in the pan, making sure all the bread is moistened. Then, spread the mixed berries evenly over the top. Gently press down if needed to help everything soak. Cover the pan with plastic wrap or foil, and refrigerate overnight so the bread can fully absorb the custard.

The next morning, remove the pan from the refrigerator. Preheat your oven to 350°F (175°C). Uncover the pan and place it on the center rack. Bake for 1 hour, or until the bread is lightly golden and the casserole is set. Let it cool briefly before serving. You can enjoy it warm or cold—personally, I love it best slightly warm with a drizzle of extra maple syrup on top.