Rub the cheese through a sieve to make smooth. Whip the heavy cream to stiff peaks with the sugar and fold into the cheese. Add lemon zest if using. Beat the egg whites to stiff peaks and fold them in to the mixture as well. Turn the mixture into cheesecloth-lined heart molds (these are porcelain with perforated bottoms, available in specialty kitchenware shops.) Set on a rack set in a casserole dish or on a baking pan, cover and refrigerate overnight to drain.
Just before serving, unmold. Serve with more sweetened heavy cream poured over, and berries.
Cook's Note: If you do not have a coeur a la creme mold, simply line a fine mesh sieve with cheesecloth and set over a bowl. It may not be heart-shaped but it will taste just as delicious.
Food Network Kitchens suggest caution in consuming raw and lightly-cooked eggs due to the risk of Salmonella or other food-borne illness. To reduce this risk, we recommend you use only fresh, properly-refrigerated, clean, grade A or AA eggs with intact shells, and avoid contact between the yolks or whites and the shell. For recipes that call for eggs that are raw or undercooked when the dish is served use shell eggs that have been treated to destroy Salmonella, by pasteurization or another approved method.