1. The night before: Spray a 9×13″ casserole dish with non-stick spray or grease with softened butter. Slice the bread loaf into 1″ cubes, and spread half the cubes into the bottom of the dish.
2. In the bowl of a stand mixer fitted with the paddle, or using an electric handheld mixer, beat together the cream cheese, powdered sugar, 1 tbsp cinnamon and vanilla extract until smooth. Drop the mixture, one spoonful at a time, throughout the scattered cubes of bread. Place the rest of the bread cubes over the top the dish.
3. Whisk together the eggs, milk and brown sugar and pour this over the bread cubes in the casserole dish, making sure that each piece of bread is moistened by the egg. Cover the dish tightly with plastic wrap or aluminum foil and place in the fridge for overnight.
4. The next morning: Remove the casserole dish from the fridge and preheat the oven to 350F. Once heated, place the dish in the oven and bake for 45-50 minutes, until the liquid is set and the bread is slightly browned. If the bread is becoming too brown while baking, lightly cover the top of the dish with aluminum foil.
5. While the dish is baking, prepare the cinnamon sugar topping. In a microwave-safe dish, melt the butter, then add the brown sugar and cinnamon, whisking to thoroughly combine. Set aside and prepare the cream cheese frosting. In the bowl of a stand mixer fitted with the paddle attachment, or using a handheld electric mixer, beat the softened cream cheese with the powdered sugar and milk until the consistency is smooth and fairly runny. Add more milk or powdered sugar to achieve the desired consistency.
6. Once the casserole comes out of the oven, drizzle both the cinnamon sugar topping and cream cheese frosting**** over the top of it, and serve immediately.

Leftover casserole can be stored in an airtight container in the fridge for 2-3 days, and reheated in the microwave.