Peel the garlic and press it through a garlic press. Stir mayonnaise, sour cream and garlic until smooth. Season with salt and cayenne pepper. Wash the parsley, dab dry and, except for a few leaves for garnishing, pluck off.
Chop finely and stir into the garlic mayonnaise. Peel the onion and remove the flower attachment. Place in an onion blossom maker and cut with a knife (or, if you do not have an onion blossom maker, make 16 cuts with a knife offset to just before the stem), so that one flower emerges.
Cook the onion in boiling water for about 2 minutes. Quench in cold water. Heat the frying fat. In the meantime stir 100 ml cold water and flour until smooth. Dab onion dry and dust with flour.
Dip into the flour mixture and deep-fry for about 5 minutes. Arrange on a plate and remove the onion heart. Garnish with chilli and parsley. Texan salsa is also delicious with it.