Pancakes with potatoes and herring sauce

You will need: 15 -17 thin pancakes baked according to your favorite recipe, 0.5 kg of potatoes; 30 g butter; milk; salt, pepper (to taste)
For the sauce: herring fillet (preferably not very salty) - 200 g; sour cream (20%) - 200 ml; lemon juice
Preparation:
Peel the potatoes, boil until tender. Make a puree by adding butter, milk, salt and pepper.
For the sauce, grind the herring fillets in a blender, add sour cream and a few drops of lemon juice.
Stuff pancakes with potatoes, fry in olive oil or butter. Serve with herring sauce. Sprinkle the pancakes with chopped green onions if desired