Cut the falukorv or sausage into thin strips or small cubes.
Chop the onion finely. Heat the oil or butter in a large skillet over medium heat.
Add the sausage and cook until it starts to brown. This should take about 3-4 minutes.
Add the chopped onions to the pan and sauté until they become translucent, about 2-3 minutes.
Stir in the tomato paste, chilli sauce and mustard mixing well to coat the sausage and onions.
Combine the milk, cooking cream and cream fraiche in a separate bowl.
Pour in the above cream mixture. Stir to combine all the ingredients.
Lower the heat and let it simmer for about 5-10 minutes, allowing the flavours to meld together.
If the sauce is too thin, you can mix a tablespoon of cornstarch in 1 tablespoon of water and add to it. Simmer for another 5 minutes.
Season with salt and pepper to taste. Remember that the sausage may already be salty, so taste before adding more salt.
Serve hot over rice, pasta, or potatoes. Garnish with chopped fresh parsley or dill if desired.