Position a rack in the center of the oven and preheat to 400 degrees. Lightly butter six 6-ounce ramekins, dust with sugar and place on a baking sheet.
In a small bowl whisk together the flour, lemon rind and poppy seeds; set aside.
In the 4-1/2 quart bowl of a heavy-duty electric mixer using the wire whip attachment, whip the egg yolks and sugar until the mixture is pale and forms a ribbon when the whip is lifted.
Place the egg whites in a medium grease-free bowl and using a hand-held electric mixer whip the whites to soft peaks.
Fold the flour mixture into the yolk/sugar mixture then add the melted butter and gently mix until combined. Fold in the egg whites until combined. Fill each of the prepared ramekins 3/4 full and place a 1-ounce piece of chocolate in the center of the batter.
Bake for 15 minutes or until firm. Cool on a wire rack for 5 minutes. Gently invert the cake onto a dessert plate and serve warm
