First make the frosting by beating together the butter and cream cheese with an electric mixer.
With the mixer on low speed, add the powdered sugar a cup at a time until smooth and creamy. Beat in the vanilla extract.
Put frosting in piping bag or plastic baggy with a corner cut.
Prepare cake according to box directions. Let cool to room temperature, then cut the cake in half, then cut the two halves into 1 inch slices to make little rectangles.
Heat 3 inches of oil to 350 degrees F.
Place a rectangle of cake in the center of the egg roll wrapper.
Squeeze a line of frosting next to the cake on the egg roll wrapper.
Dab your finger with a little water and run it along the edges of the egg roll wrapper.
Fold the bottom corner of the wrapper up and over the cake, then fold in the right and left sides. Roll the egg roll away from you to seal it up.
Repeat with the remaining cake rectangles.
Fry in the hot oil for 2-3 minutes or until golden brown.
Remove from oil to paper towels to drain.
Optional: drizzle with more frosting.