Sugar-Free Banana Cream for Cakes

Ingredients:

50g butter 🧈
5 bananas or plantains (500g) 🍌
1/2 lemon (30ml) 🍋
300ml milk (hot or cold) 🥛
50g cornstarch (can be replaced by 100g flour) 🌾
3 egg yolks 🥚
1 teaspoon vanilla essence 🌼
500ml very cold cream (milk cream or vegetable cream) 🥄
Instructions: