In a medium bowl, combine Emmentaler and Gruyere cheeses. Let stand at room temperature for 30 minutes. Add cornstarch; toss gently to combine. Set aside.
Rub the inside of a Dutch oven or fondue pot (whichever you use to serve the fondue) with the halved garlic clove. Discard garlic.
In the same Dutch oven, heat wine over medium heat until small bubbles rise to the surface. Just before the wine boils, reduce heat to low and stir in cheeses, a little at a time, stirring constantly and making sure cheese melts before adding more. Stir until mixture bubbles gently. Stir in Kirsch (if desired), pepper, and nutmeg.
If using a fondue pot, transfer cheese mixture to fondue pot. Keep mixture bubbling gently over an outdoor grill, open flame, or a fondue burner. (If mixture becomes too thick, gradually stir in a little additional wine.) Fit chunks of country bread onto long skewers or clean small tree twigs. Dip bread into cheese mixture. Makes 8 servings.