Bring Grape Juicy Juice® 100% Juice to a boil in a small saucepan over medium-high heat. Continue boiling for 20 minutes, until Grape Juicy Juice® 100% juice has reduced to 1 cup. Remove from heat, and let cool for 5 minutes.
Whisk together water and arrowroot powder in a small bowl until dissolved. Add mixture to juice, and return to medium heat, whisking continuously until juice has thickened to a syrupy consistency, about 3 minutes. Remove from heat.
Spread 4 slices of bread with peanut butter, and top with another slice of bread to form sandwiches.
Whisk together eggs, milk, vanilla extract and salt in a large mixing bowl.
Melt half of butter in a large nonstick skillet over medium heat. When butter is melted, dip two sandwiches into egg mixture until bread is well saturated on both sides. Add sandwiches to pan with melted butter, and cook until both sides are golden brown, about 3 minutes per side.
Transfer to a plate and keep warm. Repeat process with remaining butter and sandwiches.
Serve immediately, topped with powdered sugar (if desired) and grape syrup.