Make two thirds of the dill with the buttermilk in a hand mixer to a puree, season and put to cool.
Separate the cucumber from the skin, cut in half and pit with a small spoon. Peel, skin, halve and pit the tomatoes. Cut cucumber and tomato pulp into tiny cubes and drain in a colander. Chop remaining dill and whip whipping cream until stiff.
Stir the diced cucumbers and tomatoes and the dill into the buttermilk mix and fold in the whipped cream.