Grease the 9x13 inch baking dish with butter or cooking spray to prevent sticking.
Arrange the 12 slices of bread in a single layer in the baking dish, overlapping slightly if necessary.
In a mixing bowl, whisk together the eggs, milk, heavy cream, sugar, vanilla extract, cinnamon, and salt until well combined.
Pour the egg mixture evenly over the bread, ensuring that each slice is soaked. Use a fork or the back of a spoon to gently press the bread down to absorb the liquid if necessary.
Cover the dish tightly with plastic wrap or aluminum foil and refrigerate overnight (or for at least 2 hours).
When ready to bake, preheat the oven to 350°F (175°C).
Remove the covering from the baking dish and bake the French toast in the preheated oven for 40 minutes, or until the top is golden brown and the egg mixture is set.
Let the French toast cool for a few minutes, then slice and serve, drizzled with maple syrup and topped with fresh berries if desired.