In the meantime, boil the peas until tender in a pot with salted water.
Add 200 ml water from the peas into a bowl for later use, then drain the rest.
Use an immersion blender to mash the peas, while adding the butter, the water, a few lemon juice drops and seasoning to taste.
Add the peas to a sieve and by using the back of a ladle, push the content through the sieve. This way, you will obtain a far smoother composition, but you can skip this step if after using the immersion blender you are satisfied with the texture you got.
Cool down the obtained puree so that the color doesn't fade by adding it to a container with a lid, then immersed it under cold running water, then put it in the fridge until serving.