Place the cream cheese and 1 tablespoon of the maple syrup in a small bowl and mix well with a fork until smooth.

Whisk together the milk, eggs and vanilla in a shallow dish until well incorporated.

Carefully slice each piece of challah almost all the way in half, leaving the bread intact along one or two edges so that a pocket is formed. Spread a quarter of the cream cheese mixture inside each bread pocket, then stuff each of the pockets with about 2 tablespoons of grapes and press lightly to seal shut.

Spray a cast-iron or non-stick skillet with cooking spray and heat over a medium heat. Dip each piece of stuffed bread into the milk-egg mixture until well coated, then place in the skillet and cook until golden brown, about 3 minutes per side. Serve topped with the remaining grapes and drizzled with the remaining maple syrup.