In a mixing bowl (or in your blender), combine the milk, eggs, vanilla and lemon zest. Whisk (or blend) to fully combine.
In a 9x13 baking dish, add the cubed bread + cut up cream cheese in an even layer.
Pour the milk + egg mixture over the cubed bread + cream cheese. It will almost completely submerge all the bread. I use a spatula to gently press the cubed bread into the milk + egg mixture. Cover and refrigerate overnight (at least 8 hours, or up to 48 hours).
In the morning, bake at 350ºF uncovered for 1 hour, or until the top of the french toast casserole is getting golden brown. Let it cool for 5 minutes before serving.
Just before serving, make the lemon maple syrup by combining the lemon juice, maple syrup and melted butter.
Scoop and serve topped with fresh blueberries and drizzled with the lemon maple syrup.
Leftovers will keep in an airtight container refrigerated for at least 5 days.