Combine ricotta cheese, fresh blueberries, lemon zest, and powdered sugar in a medium bowl until smooth.

In another bowl, whisk together eggs, whole milk, vanilla extract, and ground cinnamon until well combined.

Spread the ricotta mixture on four slices of bread and top with the remaining slices to create sandwiches.

Heat a skillet over medium heat, add butter or oil, dip each sandwich in the egg mixture, and cook for 3-4 minutes on each side until golden brown.