Clean the beef liver from films and veins, rinse and dry. Cut the liver into portions 1.5 cm in size. Peel and rinse the onions and carrots, cut the onions and carrots for broth into 1x1 cm cubes, finely chop the onions for baking. For serving, sort out the dill, rinse, dry and finely chop. Prepare pots with lids for baking.
Cook the broth. Place a pan of water on the fire, bring to a boil, add salt, bay leaf, black peppercorns and allspice. Add onions and carrots, reduce heat. Add the ground beef and gently mix it with the vegetables and bring to a boil. Reduce heat again, cover and simmer for 40 minutes, skimming occasionally. Remove the broth from the heat and strain through cheesecloth.
Prepare ingredients before baking. Heat 1/3 of the specified volume of butter in a frying pan and fry the liver for 3 minutes over medium heat. Fry the onion in a separate frying pan in another third of the butter for 5 minutes until golden brown. Add tomato puree to the onion, stir and boil for 2 minutes, add salt.
Cook the spaghetti. Boil water, add salt and add the remaining butter. Then cook the spaghetti in boiling water for 3 minutes. Drain the spaghetti in a colander.
Bake the spaghetti in the oven. Preheat the oven to 190 degrees. Place the ingredients in the pots in the following order: first the liver, then the spaghetti, then the onions. Pour in the broth, leaving 2-3 cm to the edges, and place in the oven. To make the dish juicy, cover the pots with lids. Simmer in the oven for about 20 minutes.
Place the pot on a small board, open it, stir the spaghetti, sprinkle chopped dill on top. Place a bowl of cream sauce nearby.