1 (18.25 ounce) box yellow or pineapple cake mix
1 small box vanilla instant pudding
3/4 cup vegetable oil
1 (12 ounce) can 7-Up, at room temperature
1 cup granulated sugar
1 heaping teaspoon cornstarch
1/2 cup margarine
1 (No. 2) can crushed pineapple
1 1/2 cups flaked coconut
1 teaspoon vanilla extract
1 cup coarsely broken pecans
Beat all ingredients together well for 2 minutes with electric mixer.
Pour batter into 3 (8-inch) layer pans or a 15 x 10-inch jellyroll pan that has been greased and floured.
Bake at 325 degrees F for 25 to 30 minutes.
Cool for 10 minutes, if in layer pans, and remove from pans to cool thoroughly on wire rack.
Fill and frost.
Filling: Combine first 6 ingredients and cook over medium heat until thick.
Remove from heat and add vanilla extract and pecans. Cool before spreading between layers and over cake.
If using a 15 x 10-inch pan, leave cake in pan and spread frosting over top.