Melt the butter in a skillet over medium heat. Add the diced apples, brown sugar, cinnamon, nutmeg, and lemon juice, then cook for 5–7 minutes, stirring occasionally, until the apples begin to soften while retaining some texture.

Stir together the cornstarch and water in a small bowl to make a smooth slurry. Add it to the skillet and cook for about 1 minute, stirring until the apple mixture thickens.

Remove the filling from the heat and cool it for at least 10–15 minutes. The mixture should be cool enough to handle and thick enough that it does not release excess liquid into the wrappers.

Place one wrapper in a diamond shape and put approximately 2 tablespoons of apple filling in the lower center. Fold the bottom corner over the filling, fold in both side corners, and roll tightly toward the top corner.

Moisten the final corner with water and press it firmly to seal. Keep the finished egg roll covered while you assemble the remaining pieces so the wrapper edges stay pliable.

Heat 1 quart of neutral frying oil to 350°F (175°C). Fry the egg rolls in small batches for approximately 2–3 minutes total, turning once, until crisp and golden brown.

Transfer the fried egg rolls to a wire rack or paper towels to drain. Dust with powdered sugar or serve immediately with caramel sauce, cinnamon sugar, and vanilla ice cream.