In a large mixing bowl, whisk together the eggs, whole milk, heavy cream, granulated sugar, vanilla extract, cinnamon, and salt until well blended.
Arrange the slices of French bread in a 9x13 inch baking dish, overlapping them slightly.
Pour the egg mixture evenly over the bread, ensuring each slice is coated.
Cover the dish with plastic wrap and refrigerate overnight (or at least 8 hours) to allow the bread to soak up the custard mixture.
Preheat your oven to 350°F (175°C).
Remove the plastic wrap and bake the French toast for 30 minutes, until puffed and golden.
If desired, sprinkle the brown sugar evenly over the top and broil for an additional 1-3 minutes until the sugar melts and forms a caramelized crust. Watch closely to avoid burning.
Allow it to cool for a few minutes before slicing and serving. Optionally, serve with fresh berries or maple syrup.