Cut the onion and carrots into fine cubes. Heat the oil, sauté the onions until translucent, add the carrots and sauté for 5 minutes.
Add the tomatoes and bring to the boil briefly. Add spices, if necessary puree everything to a fine sauce with the hand blender. I prefer it in pieces. Then stir in the sour cream.
Cook the spaghetti according to the instructions on the packet and serve with it.