Whisk whole egg, 2 egg whites, granulated sugar, lemon zest & lemon juice in a medium nonreactive saucepan (see Tips). Add butter & cook over low heat, whisking constantly, until the mixture is thick enough that drawing your finger across a coated spoon leaves a mark, 5 - 12 minutes. Do not let the sauce come to a simmer. Pour the hot curd through a fine meshed sieve into a small bowl, pressing on the solids. Let cool slightly & refrigerate until chilled, about 4 hours.
Preheat oven to 250 degrees F. Line a large baking sheet with parchment paper. Draw a 9" circle with a pencil in the center of the paper to use as a guide for your pavlova, then turn the paper over so it’s pencil side down.
3Beat 4 egg whites, cream of tartar & salt in a large bowl with an electric mixer on medium speed until soft peaks form. Increase the mixer speed to high & gradually beat in superfine sugar. Continue beating until stiff & glossy. (See Tips)
4Use the back of a spoon or a rubber spatula to spread the meringue into a 9" circle (using the guide) on the parchment. Smooth & level the center & make the edges slightly higher so there is a shallow depression in the middle. (It does not have to be completely smooth). Bake the meringue for 1 hour.
5Reduce the oven temperature to 200 degrees F. & continue baking for 1 hour more. The meringue should feel firm when gently touched.
6Turn off the oven, leave the door ajar & let the meringue sit in the oven until cool, about 1 hour. (As it cools, the exterior will crack in spots).
Just before serving, whip cream in a small bowl with an electric mixer until starting to thicken. Add confectioners’ sugar & continue whipping until soft peaks form.
Use a large spatula or chef’s knife to carefully separate the meringue from the parchment & slide it onto a large flat serving platter. Fill the center depression with the lemon curd & pile the whipped cream in the center of the curd. Cut into wedges with a sharp knife. Serve immediately.
9TIP & NOTE:
TIPS: To bring an egg to room temperature, submerge it (in the shell) in a bowl of lukewarm (not hot) water for 5 minutes. A nonreactive bowl, pan or baking dish stainless-steel, enamel-coated or glass—is necessary when cooking with acidic foods, such as lemon, to prevent the food from reacting with the pan. Reactive pans, such as aluminum & cast-iron, can impart off colors &/or flavors. When egg whites are beaten to “soft” peaks, the whites will still be soft enough to curl over when a beater is turned upside down. The whites are considered “stiff” peaks when they remain stiff & upright.
NOTE: Superfine sugar is sugar that dissolves instantly. It is available in the baking section of most supermarkets, but if you can’t find it, process regular granulated sugar in a food processor or blender until ground very fine.