Prepare the Blueberry Filling : In a small saucepan, combine the blueberries, sugar, lemon juice, and 5 tablespoons of water. Cook over medium heat until the blueberries start to release their juices. Add the cornstarch slurry (cornstarch mixed with 2 tablespoons of water) to the saucepan. Cook and stir until the mixture thickens to a jam-like consistency. Remove from heat and let the blueberry filling cool completely.

Make the Cream Cheese Filling : In a medium bowl, beat the cream cheese, sugar, and vanilla extract until smooth and creamy. Set aside.

Assemble the Egg Rolls Lay an egg roll wrapper on a clean surface, with one corner pointing towards you (a diamond shape). Spread about 1 tablespoon of the cream cheese filling in the center of the wrapper, then top with a tablespoon of the blueberry filling. Fold the bottom corner of the wrapper over the filling, then fold in the sides and roll tightly. Moisten the top corner with a bit of water to seal the egg roll. Repeat for all wrappers.

Fry the Egg Rolls : Heat the vegetable oil in a deep skillet or pot to 350°F (175°C). Fry the egg rolls in batches for 2-3 minutes on each side, or until golden brown and crispy. Remove and drain on a paper towel-lined plate.

Dust and Serve : Once slightly cooled, dust the egg rolls with powdered sugar. Serve warm, optionally with a side of whipped cream or a blueberry dipping sauce.