Instructions:
Preparation: Generously butter a 9×13-inch baking dish. Arrange the bread slices in the dish in two rows, overlapping if necessary.
Egg Mixture: In a mixing bowl, whisk together the eggs, milk, heavy cream, sugar, vanilla extract, cinnamon, and lemon zest until fully combined.
Assembly: Pour the egg mixture evenly over the bread slices, ensuring all pieces are coated. Scatter the blueberries across the top, tucking some in between the slices as well.
Refrigeration: Cover the baking dish tightly with plastic wrap and refrigerate overnight, allowing the bread to soak in the egg mixture.
Baking: The next morning, preheat your oven to 350°F (175°C). Remove the plastic wrap and bake the French toast for 45-50 minutes, until golden brown and set.
Finishing Touches: Let it cool slightly, then dust with icing sugar if desired, and serve warm.
