Cake
1 (18.25 ounce) box devil's food cake mix
1 (3.9 ounce) box instant chocolate pudding mix
4 eggs
1 1/4 cups water
1/2 cup vegetable oil

Filling
1/4 cup all-purpose flour
1 cup milk
1/2 cup shortening
1/2 cup butter
1 cup granulated sugar
2 teaspoons vanilla extract

Glaze
1 cup chocolate chips
1/4 cup shortening
3 tablespoons light corn syrup
2 1/4 tablespoons water

Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 10-inch springform pan.

Cake: In a large bowl, stir together the cake mix and instant pudding. Make a well in the center and pour in the eggs, oil and water. Mix until well blended. Spread evenly into the prepared pan. Bake for 45 to 50 minutes in the preheated oven, or until a wooden pick inserted into the center comes out clean. Cool cake completely on a wire rack before removing from pan.

Slice a 1-inch thick slice off of the top of the cake and set aside. Scoop out the cake for the center of the bottom part to within 1 inch of the sides. Discard or save for another use.

Filling: Whisk together the flour and milk. Cook over medium heat, stirring constantly until thickened. Set aside to cool completely.

Once the flour and milk mixture has cooled, beat the 1/2 cup shortening, butter, sugar and vanilla extract on high speed until light and fluffy. Add the milk mixture and continue to beat for 4 more minutes. Spoon into the center of the cake and replace the layer sliced from the top.

Glaze: Combine the chocolate chips, 1/4 cup shortening, corn syrup and water in the top of a double boiler. Heat, stirring frequently until melted and smooth. Pour warm glaze over the top of the cake and smooth over the sides. Refrigerate until ready to serve.