Grease a 9x13 baking dish or casserole dish with baking spray.
In a medium pot, over medium heat, melt together the butter and ½ cup brown sugar until it begins to simmer, stirring often. Turn off the heat and pour the hot butter-sugar mixture into the greased pan, spreading into an even layer. Set aside.
Next, mix together the remaining ½ cup brown sugar and cinnamon in a small bowl and set aside for later.
In a large bowl, using a handheld electric mixer or whisk, beat the cream cheese until creamy and smooth, about 2 minutes.
Slowly add the maple syrup and beat until it has loosened the cream cheese. Add the eggs, one at a time, and beat until smooth and combined.
Finally, mix in the milk, heavy cream, vanilla extract, and salt, until combined and mostly smooth for 1-2 minutes. It’s ok if there are a few small cream cheese chunks that remain. *Alternatively, place all the ingredients in steps 4-6 into a blender and blend for 30-60 seconds, until smooth. Tear each piece of bread roughly into quarters (4 pieces per slice).
Place about ⅓ of the torn bread pieces in an even layer at the bottom of the pan. Spoon 2 cups of the egg-cream mixture over the bread, spread into an even layer. Then, sprinkle 2 1/2 tablespoons of the sugar-cinnamon mixture over the entire top.
Repeat with another ⅓ of bread pieces, 2 cups egg mixture, 2 1/2 tablespoons sugar-cinnamon mixture, remaining bread pieces, remaining egg mixture, and remaining sugar-cinnamon mixture. Use your spoon or hands to press down on the liquid and bread in the pan to help move things around and compact the ingredients.
Cover the pan with foil and refrigerate for at least 3 hours, if possible.
Preheat the oven to 350°F.
Bake, covered, for 30 minutes.
Carefully remove the foil and bake uncovered at 375°F for another 20 minutes. The casserole should look puffed up and lightly crisp on the bread edges.
Allow to cool for 10 minutes and enjoy!