Peel and wash the potatoes. Cover and cook in boiling salted water for about 20 minutes. After 10 minutes of cooking, add the frozen peas and cover and cook for about 10 minutes.
Drain the potatoes and peas in a sieve and then press them through a potato press.
Put milk, cream and butter in a saucepan and warm up. Stir in the squeezed potatoes. If necessary, add some cream or milk.