Preheat oven to 350. Mix up the yellow cake mix following directions on box. Pour into two 8 inch parchment lined round cake pans. Bake according to box directions 30-35 minutes. Remove and let cool.
PB Custard-In a medium bowl pour your two kinds milk. In a small saucepan combine your sugar, butter and 1/2 cup of the milk mixture and heat just to warm it and then remove from heat.
Now Separate your egg yolks in a small bowl and add them to the bowl of uncooked milks and stir in your cornstarch, then add your warmed milk mixture and whisk. Put this mixture into a medium saucepan and cook over medium heat until thickened.
Remove from heat and add 3/4 cup peanut butter blend until smooth. Place the custard in the refrigerator to cool. While waiting for custard & cakes to cool, mix your tub of cool whip with your 4 Tbsp. of peanut butter and mix well. put lid back on and put in the refrigerator.
Peel your parchment from cake bottoms and place first layer top down. Add half of the custard and spread evely. Then place next layer top up and spread other half of cold custard evenly. Spread cool whip on sides then on top. Set back in refrigerator 2 hours. This makes a light & creamy, soft & delicious cake. Enjoy!