Scald tomatoes, peel, remove seeds and cut into strips. Wash and cut leek.
To make sauce heat vegetable oil. Stir-fry leek. Sprinkle with flour, add crushed bouillon cube. Add 4/5 cup water, stirring, tomato puree, vermouth, lemon juice and yogurt. Stew for several minutes. Season with salt and pepper.
Boil tagliatelle in much salted water (1:6), drain and dress with butter.
Mix rock lobster tails, tomatoes and the sauce, warm without boiling. Serve with tagliatelle.
