Ultimate Easy Pineapple Cake

1 (18.25 ounce) box yellow cake mix
1 (20 ounce) can crushed pineapple (do not drain)
1/2 cup (1 stick) butter or margarine
1 1/2 cups granulated sugar

Prepare yellow cake mix as directed on box, reserving 1 cup of batter for cake topping. Bake in a 13 x 9-inch pan. While cake is baking, prepare topping.

Topping: Mix undrained pineapple, butter, granulated sugar and 1 cup reserved cake batter in a large saucepan. Cook and stir over low heat until it begins to thicken. Pour over hot cake.