Spread the white truffle butter on the bread slices. Thinly slice the taleggio cheese. Spread half of the cheese amongst 4 slices of bread. Add the ham and cover with the rest of the taleggio cheese. Close the sandwiches with the other slices of bread.
Place on a baking sheet. Place under the broiler for 6 minutes, turning halfway through cooking.
Meanwhile, thinly shave the white truffle.
Once out of the oven, cut each croque-monsieur into 3 pieces lengthwise. Arrange the white truffle slices on top and serve immediately.