For the crostini with steamed lettuce hearts, fry the bread slices in a little olive oil until golden brown on both sides. Lift out, drain on a paper towel and keep warm. Cut the lettuce hearts in half and slice the garlic.
Heat about 1 tablespoon of butter in a frying pan and sauté the garlic briefly. Place the lettuce hearts cut side down, add sweet wine and let steam for about 2 minutes, covered. Season with salt, pepper and balsamic vinegar. Place the still warm crostini on preheated plates. Arrange the lettuce hearts on top and add the slices of ham decoratively.