Wash the carcasses thoroughly under cold running water. Chop the yellow beets, celery, leek and tomatoes into coarse pieces. Also chop the shallots and garlic. Heat 2 tablespoons of oil in a large saucepan and brown the carcasses. Deglaze with cognac as well as beer and boil down. Remove from the heat. Heat the remaining oil in a second pot and sauté the prepared vegetables with herbs, spices and tomato paste. Add to the carcasses, stir in the butter and brown. Season with salt and pepper and add 2 liters of water. Simmer gently for about 50 minutes, skimming off the foam that forms several times. Strain the stock through a sieve lined with a straining cloth. After cooling, skim off the fat.
Preparation Tip:
If this lobster stock is to be used for a bisque (lobster bisque), add a little Noilly Prat or white wine, allow the stock to boil down again and then add cold butter to the soup.