Filling:
9 very ripe bananas
1/2 cup sugar
1/4 cup milk
1 stick butter (real butter, not margarine)
Mash bananas in a heavy pan or pot. Add remaining ingredients and cook over very low heat for 45 minutes.
Cake:
1 box butter cake mix
Prepare per instructions on the box, but make 5 (that’s right, 5) layers. You can use 5 pans with a small amount of batter evenly divided among them, or 3 pans, one with a small amount of batter and two with more batter. These two layers you can split, making a total of 5 layers.
While banana filling is warm, spread filling between warm cake layers while banana mixture is warm. Stack the layers and spread the remaining filling on the top layer.