Preheat your slow cooker to low. Lightly grease the interior with nonstick cooking spray or a thin layer of melted butter to prevent sticking.

In a large glass bowl, whisk together the eggs, milk, vanilla extract, salt, and cinnamon until the mixture is completely smooth and uniform in color.

Arrange half of the bread slices in a single layer inside the slow cooker insert, pressing down gently to create a flat surface.

Pour half of the egg custard over the bread, using a ladle to distribute evenly. Sprinkle half of the cinnamon sugar mixture over the soaked bread.

Layer the remaining bread slices on top, then pour the remaining custard over everything. Sprinkle with the remaining cinnamon sugar.

Cover the slow cooker and cook on low for 3 hours, or until a knife inserted into the center comes out clean and the edges are golden brown.

While the French toast is cooking, combine the maple syrup, butter, and powdered sugar in a small saucepan over low heat. Stir constantly until the butter is melted and the mixture is smooth and glossy, about 2 minutes.

Remove the French toast bake from the slow cooker and let it rest for 5 minutes to set. Drizzle the warm maple glaze evenly over the top before serving.