Grandmomma's Lemon Apple Filling

3 apples, grated
juice of 2 lemons
2 t lemon zest or 1 t dried lemon peel
1 C sugar
1/2 stick margarine
1 egg yolk

Mix all ingredients and cook over medium heat until thick.

Grandmomma used this on plain yellow or white cakes.

http://recipecircus.com/recipes/vishusvi/CAKESandPIES/Grandmomma39s_Lemon_Apple_Filling.html