Cut the onion in half and roast over moderate heat in a dry frying pan until soft. Finely chop.
Finely chop the green onion and rub with salt to extract the juice. Mash the garlic with a pinch of salt into a paste.
Finely chop the dill. Bread cut or break into pieces.
Place bread, sliced baked and green onions, garlic paste and dill on a plate. Pour in kvass, garnish with sour cream and serve.