Preheat the oven to 350F and spray an 8 x 8-inch baking dish with cooking spray and set aside.

In a large bowl whisk together the milk, heavy cream, eggs, sugar, vanilla extract, banana extract and salt. Add the croissant cubes and mix together until the croissants are fully coated in the cream mixture. Let it sit for 25-30 minutes, stirring about 15 minutes in. Once the croissants have soaked pour the mixture into the prepared pan. Nestle in the banana slices.

Bake for 45-50 minutes, until the custard is set and the croissants are starting to brown. After the casserole has finished baking, let sit for 10 minutes before serving.