In a medium-sized saucepan over medium heat, combine the apple cubes, lemon juice, cinnamon, and sugar. Stir the mixture until the sugar dissolves.

In a separate small bowl, mix the cornstarch with 1/3 cup water until smooth, then pour it into the saucepan. Stir the mixture and bring it to a boil. Once boiling, reduce the heat to a simmer, cover, and cook until the apples are just tender and the sauce has thickened, about 5 minutes.

Remove the pan from the heat and stir in the vanilla extract. Transfer the apple filling to a bowl and let it cool completely.

Prepare a small bowl of water and line a baking sheet with paper towels.

Once the filling has cooled, place the egg roll wrappers on a clean work surface. Using a slotted spoon, place about 1/4 cup of the apple filling onto the lower third of each wrapper. Start rolling from the bottom, folding in the sides as you go. Dip your finger in water and wet the edges of the wrapper to seal the egg rolls tightly.

In a large, heavy-bottomed pot, pour in enough oil to reach a depth of about 4 inches. Heat the oil over medium-high heat until it reaches 360°F. Fry 3 to 4 egg rolls at a time, turning them occasionally, until they are golden brown, about 2-3 minutes. Remove the fried egg rolls and place them on the prepared baking sheet to drain. Repeat with the remaining egg rolls, ensuring the oil returns to 360°F between batches.

Serve the egg rolls hot with whipped cream or caramel sauce if desired.