In a large bowl, whip the cream until stiff. In a medium bowl, beat the egg whites until stiff. Gently fold the whites into the whipped cream.
In a medium bowl, whisk together the egg yolks and sugar until thick and pale. Whisk in 1 cup of the blueberries and the mint, beating until most, but not all, of the berries burst and the mixture turns dark violet. Fold the blueberry mixture gently into the whipped cream.
Transfer the parfait mixture to a 1½-quart mold, or leave it in the bowl. Cover with plastic and place in the freezer for at least 8 hours.
Forty minutes before serving, transfer the parfait to the refrigerator.
To serve, place the mold in warm water for a few seconds and invert the parfait onto a serving plate. Garnish with the rest of the berries and the chocolate and serve immediately.