The meringues can be made up to a day ahead of time and stored in airtight containers. Save your egg yolks in the fridge covered with a little cold water to make lime curd. Serves 10.
4 large egg whites
1 pinch salt
1 cup sugar
2 tsp. cornstarch
1 tsp. white wine vinegar (or plain white vinegar)
2 lbs. rhubarb, cut into 3/4-inch pieces
3/4 cup granulated sugar
1 tsp. vanilla paste or vanilla extract
1/8 tsp. cardamom
1-1/2 cups heavy cream
1 Tbsp. confectioner’s sugar
Splash of vanilla extract
Preheat the oven to 250°F. Line two sheet pans with parchment paper and trace 10 4-inch circles in pencil using a glass as a guide. Turn the parchment paper over so you can still see the circles but you don’t get pencil on your meringue.
Using an electric mixer, whip the egg whites with a pinch of salt in a large, clean bowl on medium-high speed. (It’s very important that your bowl is grease-free and that you separate your eggs cleanly, with no broken yolks mixed in with the whites. Any fat will interfere with the whipping process.) When soft peaks form, begin adding the sugar 1 tablespoonful at a time with the mixer running. Continue beating on medium-high speed until the mixture is dense and stiff, glossy peaks form, about 5 minutes. Rub some meringue on your fingers to make sure all the sugar has dissolved. It should feel smooth, not gritty. Using a spatula, lightly but thoroughly fold in the cornstarch and vinegar.
Gently spoon the fluffy mixture in the marked circles on the parchment paper, making a well in the middle of each for the filling. If the parchment is sliding around too much, use a dab or two of the mixture to glue the paper to the pan. Bake them in the preheated oven for 40-45 minutes until they’re just starting to take on some light color and feel firm on the outside but still soft in the middle. If they crack slightly, that’s okay. Then turn off the heat and let them sit inside the oven with the door propped open with a wooden spoon for 20 to 30 minutes. They should still feel soft in the middle when gently pressed. Remove from the oven and let cool completely.
Increase the oven temperature to 325°F. In a large roasting pan, toss the rhubarb with the sugar, vanilla, cardamom, and salt. Let sit for 20 minutes to draw out some moisture. Then cover tightly with foil and bake for 25 to 30 minutes until the rhubarb is soft but still holds its shape. Remove from the oven. Strain the rhubarb in a sieve set over a medium saucepan. Gently transfer the rhubarb to a medium bowl. Over medium heat, bring the rhubarb juices to a simmer and then reduce for 5 or 6 minutes until syrupy. Pour the syrup over the rhubarb and let cool, then refrigerate covered until ready to serve.
Assemble the pavlovas just before serving. Whip the cream in a clean bowl with confectioner’s sugar and a splash of vanilla until soft, smooth peaks form. Spoon the rhubarb into the wells of the cooled pavlovas and top with softly whipped cream.