In a large bowl, combine the sugar and lemon zest. With your fingers or back of a spoon, rub the lemon zest with the sugar to release its oils.

To the sugar, add the eggs and salt and whisk just a minute, until foamy and smoothly blended; the mixture should not thicken.

Spoon the flour and baking powder into a sifter and sift about a third of the dry ingredients over the foamy egg mixture. Whisk the flour into the eggs, mixing lightly. Sift the flour over the eggs in two more additions and whisk only until everything is incorporated. Whisk the heavy cream into the mixture. Fold in the melted butter.

Pour the batter into the prepared pan - it will level itself - and bake for 50 to 60 minutes (mine took 60), or until the center of the cake crowns and cracks and a toothpick inserted in the center comes out clean. Remove the cake to a cooling rack to rest for 10 minutes before unmolding. Cool to room temperature right side up on a rack.

When cool, wrap tightly with foil or plastic wrap. Cake should keep for 3 or 4 days.