Melt butter in the microwave and stir in brown sugar until well mixed.
Pour the butter and sugar mixture into the bottom of a 9x13-inch baking pan, spreading it evenly.
In a bowl, beat together eggs, milk, and vanilla extract.
Lay a single layer of bread slices in the prepared pan.
Spoon half of the egg mixture over the bread layer.
Sprinkle cinnamon generously over the bread and egg layer.
Add a second layer of sliced bread on top.
Spoon the remaining egg mixture over the top layer of bread.
Cover the dish and refrigerate overnight to allow the flavors to blend.
Preheat the oven to 350°F (175°C).
Bake the French Toast Bake for 45 minutes, covering it for the first 30 minutes to avoid over-browning.
Remove from the oven and sprinkle powdered sugar and additional cinnamon over the top.
Serve warm with maple syrup for a truly indulgent experience.