Peel and dice the onion and sweat in 1 tbsp butter until translucent. Deglaze with the vegetable stock, bring to the boil and add the frozen peas. Then bring everything to the boil again and add a little salt. The pre-cooked peas do not require any cooking time. After boiling once, simmer for 1 minute and then pour through a sieve. Catch the stock and, while pureeing with the hand blender, gradually pour in just enough of it until the puree has the consistency you want it to be. We don't like it too mushy, so please decide for yourself how much liquid you want to add. Then only season the puree with salt and pepper and fold in the remaining tablespoon of butter. It can cool down afterwards, but that's already done. But it is enough for more than 2 people, so you can freeze the rest and "bring it back to life" for the next meal.