For the pavlova, preheat oven to 350°F. Line a baking sheet with parchment paper. Using a 9-inch pan as your guide, draw a circle onto the parchment. Flip the parchment over so that the markings are face down.
Place egg whites and salt into the bowl of a stand mixer. Beat at a low speed to break up egg whites and then slowly increase to high. Beat until the mixture has a satiny appearance and soft peaks. Add sugar 2 Tbsp at a time, and continue beating until all the sugar is used and the mixture is shiny and stiff peaks form.
Gently fold in cornstarch, vinegar, and vanilla. Using the circle you drew as a guide, heap the meringue onto the parchment. Gently flatten into a disk, making the sides about ¼-inch higher than the middle will help to hold your topping and any juices that form). Place in the oven and immediately reduce heat to 300°F. Bake for 1 hour and 15 minutes.
Once done, turn off the heat and leave the meringue in the oven to cool completely. (I prefer to make pavlova in the evening, after dinner, so I can let it rest in the oven overnight. Moisture is a pavlova’s worst enemy and this ensures it won't be sticky or soggy.)
For the rhubarb, preheat oven to 350°F. Cut the rhubarb into 1-inch pieces on a bias. Place the rhubarb, honey, and Cara Cara juice into a baking dish with a pinch of salt and toss to coat the rhubarb. Bake in the oven for 20 minutes or until the rhubarb is just tender.
For assembly, place heavy cream in a chilled bowl and whip, using an electric mixer, until medium peaks form. There is plenty of sweetness in the pavlova so I prefer to not sweeten the cream for this recipe.
Mix the strawberries and rhubarb, very gently, in a medium bowl. Place the pavlova onto a platter. Fill the center with the whipped cream. Top with the strawberry-rhubarb mixture and edible flowers. Dust with powdered sugar just before serving.
A Note From Richard: Pavlova is an Aussie icon. This meringue-based dessert was named after the Russian ballerina Anna Pavlova when she completed a tour of Australia and New Zealand in the 1920s. Ella was dancing around the kitchen when she suggested adding rhubarb and strawberry to the top of this classic. There’s something magic about the addition of sour to the sweet.