Twinkie Cake

1 box Lemon Cake Mix
1/4 cup oil
1 1/2 cup water
1 pkg instant lemon pudding
2 eggs
1 cup milk
1/2 cup shortening
5 T flour
1/2 cup butter
1 cup sugar
1 tsp vanilla
1/2 tsp salt

Combine cake mix, oil, water, pudding and eggs in a mixing bowl.  Beat and pour into greased and floured 9x13 pan.  Bake according to package direction.  Remove from pan and cut horizontally while hot with string or dental floss to make 2 layers.  Do not remove top layer until completely cool. 

Cook flour and milk until thick and set aside to cool.  In a bowl whip together the remaining filling ingredients until fluffy.  Add milk and flour mixture and beat together.  Use all filing between layers of cake. 

Refrigerate for 1 hour before serving and slicing.