Herring butter for buterbrodes

Ingredients:

1 herring fillet
¼ lb butter
3 tbsp vegetable oil
1 small shallot onion.
Lemon juice on taste

Method:

Cut onions into very small cuts.
Cut fillet into small cuts.
Put them together in a mixer, then add warm butter, and blend well.
Then, add vegetable oil by the spoon continuing blending.
Optionally: add lemon juice, continuing blending.
Keep in a refrigerator.