In a heavy-based saucepan, combine chocolate, cherry brandy or kirsch, butter and corn syrup. Add 2 tablespoons sugar if using cherry brandy, 3 tablespoons sugar if using kirsch. Melt over very low heat, then scrape into a bowl and allow to cool a little.
Separate eggs, and whisk whites until soft peaks form. Beat yolks into cooled chocolate mixture, then gently mix in a dollop of egg whites to lighten mixture. Carefully fold remaining whites into chocolate mixture, taking care to keep mousse airy.
Spoon mousse into two wine glasses. Cover with plastic wrap, and refrigerate for at least 2 hours and up to 6 hours before serving. YIELD 2 servings.