Slice the tomatoes and arrange them in rosettes on a plate. Heat about a tablespoon of olive oil and sauté the chopped shallots, garlic and parsley until light, i.e. without letting them take color. Remove from heat. Pour in Marsala and balsamic vinegar. Season with salt and pepper. Pour the remaining olive oil. Spread this marinade over the tomatoes and place the Prosciutto di Parma decoratively on top. Garnish with fresh chervil.