Prepare the pasta in boiling salted water according to the instructions on the packet. Peel onion and cut into fine cubes. Wash, clean and halve the cherry tomatoes. Wash the rosemary, dab dry and pluck the needles from the twigs. Heat oil in a pot. Sauté diced onions until translucent. Add the cherry tomatoes, pine nuts, rosemary needles and tomato paste and steam for 1 minute.
Deglaze with sherry and fill up with 250 ml water. Stir in stock. Mix starch with 2 tablespoons of water, add to the liquid and bring to the boil while stirring. Season to taste with salt, pepper and sugar. Drain the noodles. Serve with sauce on plates