Wacky Abi's Twinkie Cake

I went to a pierogi party this weekend and was asked to bring a dessert. I did some research on Ukrainian desserts and...ick. No offense to all those Ukrainian blog followers I have out there, but, no thank you. So, I decided to go in the opposite direction and go hard core American. I made my first ever Twinkie cake...and NO it is not made with real Twinkies...again, ick. Read this.
My wacky sis gave me this recipe and it was great! I served it right out of the fridge and with fresh strawberries, blueberries and blackberries.

1 Box Yellow Cake Mix
Ingredients needed on back of Yellow Cake Mix Box
5 Tablespoons flour
1 Cup sugar
2 teaspoons vanilla
1 Cup water
1/2 Cup shortening
1/2 Cup margarine

1. Bake Yellow Cake according to the directions on the box in two 9" round pans.
2. Make Filling. Combine flour and water on stove top and cook until thick. Cool in refridgerator. Combine sugar, margarine, shortening and vanilla. Beat until thick and fluffy...this takes like 10-15 minutes. Add cooled mixture; beat until fluffy. If it looks curdled, just beat it a little more.
3. Once cakes are done and cooled, spread filling in between layers. You can put a little on top if your middle layer is looking a little too thick.
4. Cool in refridgerator at least one hour before serving. YUM!