Step 1: Assemble the Bread Layer

1. Preheat your oven to 350°F (175°C).
2. Grease a 9×13-inch baking dish with nonstick spray.
3. Cut the gluten-free bread into 1-inch cubes. Spread half of the bread cubes evenly in the prepared dish.
4. Scatter cubed cream cheese and blueberries over the bread layer. Top with the remaining bread cubes.

Step 2: Prepare the Custard

1. In a large mixing bowl, whisk together the eggs, milk, vanilla extract, and maple syrup.
2. Pour the custard mixture evenly over the bread layers, ensuring all the bread is soaked.

Step 3: Chill and Bake

1. Cover the dish with plastic wrap and refrigerate overnight, or for at least 4 hours, to let the bread soak.
2. When ready to bake, remove the dish from the fridge and let it sit at room temperature for 30 minutes.
3. Bake the casserole, covered with foil, for 30 minutes. Remove the foil and bake for an additional 25–30 minutes, or until the custard is set and the top is golden brown.

Step 4: Make the Blueberry Sauce

1. In a medium saucepan, whisk together the sugar and cornstarch. Gradually stir in the water.
2. Heat the mixture over medium heat until it begins to boil, stirring constantly.
3. Add the blueberries and reduce the heat to a simmer. Cook for 10 minutes, or until the blueberries release their juices and the sauce thickens.
4. Stir in the butter until melted and glossy.

Step 5: Serve and Garnish

1. Slice the casserole into squares and serve warm.
2. Drizzle each portion with blueberry sauce and garnish with fresh blueberries or a dusting of powdered sugar, if desired.