In a saucepan, combine blueberries, sugar, lemon juice, and 4 tablespoons of water. Cook over medium heat until blueberries soften.
Mix cornstarch with remaining 3 tablespoons of water to create a slurry. Stir into the blueberry mixture and cook until thickened. Remove from heat and let cool.
In a bowl, beat cream cheese, sugar, lemon juice, and vanilla until smooth.
Place an egg roll wrapper on a flat surface. Add a spoonful of cream cheese filling and a spoonful of blueberry filling in the center.
Fold the sides of the wrapper over the filling, then roll tightly. Seal the edges with a little water.
Heat oil in a deep fryer or large pot to 350°F. Fry egg rolls until golden brown, about 3-4 minutes. Drain on paper towels.
Dust with powdered sugar before serving.
Notes
For a crispier texture, ensure the oil is hot enough before frying.