The King themselves granted an audience. Meet them and offer various desserts as a gift. The more desserts King eats, the bigger they get. Should they get big enough, they will be happy, and you will be rewarded. Their appetite knows no bounds!
Accidents happen, and because of their hunger, the king may consume something unexpected. They will remove it from their mouth, but it will also get smaller, and no rewards will be granted when that happens.
You can offer deserts to King Pig whenever and how much you want, but feeding them once per single won level is also fine!
Deserts can be collected when playing levels, but they may also appear from Loot Crates.