In a big mixing bowl, whisk together eggs, milk, vanilla, and sugar until everything is nicely mixed.
In another bowl, use a whisk to combine mascarpone, ricotta cheese, and powdered sugar.
Gently fold the blueberries into the mascarpone mixture – it's the berrylicious touch!
Take slices of challah bread and spread the blueberry mascarpone goodness between them. Arrange the slices in a 12×8 oven-safe baking dish, ensuring there's a layer of the delightful mixture between each slice.
Don't forget to spread any leftover mascarpone within the gaps – we don't want to miss any of that goodness!
Pour the egg wash evenly over the challah bread slices.
Pop your masterpiece into the fridge overnight to let it soak up all the eggy goodness. If you're short on time, give it at least 30 minutes to chill.
Preheat your oven to 350 degrees – we're getting close to deliciousness!
Bake the French toast casserole for 40-45 minutes – your kitchen is about to smell amazing.
When it's done, take it out and sprinkle some powdered sugar on top before serving. Voilà! Your delightful blueberry French toast is ready to impress! Enjoy your brunch!