Cake
1 (18.25 ounce) package devil's food cake mix
1 package (4 serving size) instant chocolate pudding mix
4 eggs
1 1/4 cups water
1/2 cup oil
Filling
1/4 cup flour
1 cup milk
1/2 cup shortening
1/2 cup butter
1 cup sugar
2 teaspoons vanilla extract
Icing
1 cup semi-sweet chocolate chips
1/4 cup shortening
3 tablespoons light corn syrup
2 1/4 tablespoons water

Cake
Heat oven to 350°F. Grease and flour a 10 inch springform pan. Stir together cake mix and instant pudding. Make a well in the center and pour in eggs, oil and water. Mix till well blended. Spread evenly into prepared pan. Bake for 45-50 minutes till toothpick inserted the center comes out clean. Cool cake completely on a rack before removing from pan. Slice a 1 inch thick slice off of the top of the cake and set aside. Scoop out the center of the cake to within 1 inch of the sides, leaving a bottom thick enough that it won't break easily. Discard cake center or save for another use.
Filling
Whisk together flour and milk. Cook over medium heat, stirring constantly till thickened. Alternatively, whisk together and microwave on high for 30 seconds at a time till thickened, whisking well after each cooking period. Set aside to cool completely. Once the flour and milk mixture has cooled, beat shortening, butter, sugar and vanilla on high speed till light and fluffy. Add milk mixture and continue to beat for 4 more minutes. Spoon into center of cake and replace layer sliced from the top.
Icing
Combine chocolate chips, cup shortening, corn syrup and water in the top of a double boiler. Heat, stirring frequently till melted and smooth. Pour warm glaze over the top of the cake and smooth over the sides. Refrigerate till serving.
Nicole's Note
This can also be made in two 9 inch round pans. Bake 30 minutes, I think it was. Skip the leveling part of the cutting and scoop out the center of one cake. Spoon the filling in. On the domed side of the second cake, scoop out a shallower depression to accomodate the filling. Place, hollowed side down, on top of filling in first cake. Frost once with frosting to get smooth top. Chill to set. Wait for frosting to set up a bit and use to fill in gaps between cakes and to ice sides smooth.

The leftover cake can easily be used for cake balls.