Rub the inside surface of a fondue pot with the cut garlic halves. Light the heating element and adjust the flame to medium. Combine the wine and the remaining 2 teaspoons lemon juice in the fondue pot and bring to a simmer. In a bowl, toss together the Gruyere and cornstarch until well mixed. Gradually add the Gruyere mixture to the fondue pot, stirring constantly. Stir in the kirsch and heat without boiling until very thick, about 5 minutes.
Meanwhile, drain the apple and pear slices and arrange on a plate with the grapes. Arrange the bread cubes in another container. Stir the nutmeg into the fondue and serve immediately. Provide long forks for dipping the fruits and bread cubes.