Preheat oven to 350℉ (180℃).
Prepare a 13" x 9" cake pan by spraying with baking spray or brushing with softened butter.
Place peanut butter, water and butter in a saucepan. Heat over medium-low heat until butter is melted. Stir often.
1 Cup Water, ⅔ Cup Peanut butter, ½ Cup Unsalted butter
Remove pan from heat and set aside to cool to 5 minutes.
In a large mixing bowl, combine flour, sugar, baking soda and salt.
2 Cups All-purpose flour, 2 Cups Granulated sugar, ½ teaspoon Sea salt, 1 teaspoon Baking soda
Add eggs and milk to the bowl. Mix until well combined.
3 Large Eggs, ½ Cup Whole milk
Add peanut butter mixture and mix until well combined.
Optional - add any additional ingredients, such as chocolate chips, and stir to combine.
Pour cake batter into prepared baking pan.
Bake for 40 - 45 minutes, or until cake is fully risen and a toothpick inserted in the center of the cake comes out clean.
Place the cake on a rack and let it cool for 20 minutes — it should still be warm when you add the banana pudding.