Mix vinegar, salt, pepper and sugar well in a bowl. Beat the oil well into the mixture
Wash, quarter, seed and dice the tomatoes. Wash the herbs, shake dry and cut into strips, except for something to garnish. Peel and finely dice the onion. Mix everything with the marinade
Briefly fry the baguette slices and brush them thinly with butter. Cover with 1 slice of ham. Spread the tomato mixture on top, garnish with the remaining herbs