Prepare the bread by cubing or slicing 8 cups of stale bread into 1-inch pieces.

In a medium bowl, whisk together 2 cups of dairy-free milk, 3/4 cup of brown sugar, 1/4 cup of cornstarch or ground flaxseed, 1 tablespoon of ground cinnamon, 1 teaspoon of vanilla extract, and a pinch of black salt until smooth.

Grease a 9x13-inch casserole dish and scatter the cubed bread evenly in the dish. Pour the custard mixture over the bread.

Cover the dish with plastic wrap and let it soak for at least 30 minutes or refrigerate overnight.

Mix together the crumble topping ingredients in a small bowl until crumbly.

Remove the casserole from the refrigerator, sprinkle the topping, and bake it in a preheated oven at 350°F for 30-40 minutes.

Let the casserole cool for 5 minutes, dust with powdered sugar, and serve warm.