1. Immerse tomatoes into a pot of boiling water for 1 minute, then into a pot of cold water. Slip off skins, halve, remove seeds and cores and discard. Roughly chop the flesh.
2. Put cottage cheese, yogurt, garlic clove and dill into a bowl and combine well. Season with salt and pepper to taste. Stir in chopped tomatoes. Spoon mixture into a serving dish. Garnish with a sprig of fresh dill.
Serve the mushrooms warm, together with the dip.