Peel the onions and garlic, chop finely and sauté until transparent in olive oil well heated in a pan. Add tomato puree, salt and pepper to taste, season with sugar and flavour with a bouillon cube. Simmer the sauce, covered, for 15 minutes. Cook the sauce for the last 5 minutes on low heat without a lid.
Boil the frozen tortellini in boiling water, remove with a slotted spoon, put in a colander, rinse with cold water and let it drain. Wash the basil, carefully shake off the drops, tear off the leaves, put a few pieces aside. Finely chop the remaining basil leaves and add to the sauce. Arrange the tortellini on plates with the sauce and garnish with the remaining basil leaves.