To prepare pea puree, you need to pre-soak the peas (for about 6-8 hours).
Rinse the soaked peas, put them in a saucepan and pour water, add salt and put on fire. After the peas boil, remove the foam and put the finely chopped onion. Then reduce the heat to low and cook until tender, stirring occasionally. When the peas are cooked, add the butter and mix. Mashed potatoes are ready.