Forshmak with pickled mushrooms

The suggested recipe is, I hope, real, Jewish. A colleague introduced me to him, and her mother-in-law, a real Jewess with a very beautiful name Ethel, taught her how to cook this forshmak. According to this recipe, I cook forshmak quite often, I like it more than the more common recipe with apple and white bread.

Ingredients

• herring s / s 1 pc
• pickled mushrooms 100 gr
• onion 2 pcs
• butter 3 tbsp
• pepper
• vegetable oil

Directions

1. The proportions are approximately as follows: one part is salted herring and one part is pickled mushrooms and fried onions together. Finely chop the onions and fry until soft and light golden brown. Refrigerate. Cut the salted herring fillet into small cubes. You can buy ready-made fillets in the store. The taste of the forshmak depends on the taste and salinity of the fish, so I strongly advise against taking salted or rusty herring.
2. Cut the pickled mushrooms into small cubes.
3. The fried onions have cooled down. Add it to fish and mushrooms.
4. Add mild butter for flavor. Pepper to taste. Forshmak is already good and tasty, so this step is not necessary, but with butter it turns out to be very soft and delicate in taste. Not much, just a couple of tablespoons. Mix well. If the forshmak stands, it will become more intense and interesting, as all the ingredients will exchange flavors.