Make the Pistachio Pavlova:

1. Preheat oven to 350° F.
2. In a small bowl, toss the pistachios and cornstarch.
3. In the bowl of a stand mixer fitted with the whisk attachment, beat the egg whites and salt on high until foamy, 2 minutes. Beat in the vinegar.
4. Beat in the sugar 1 tablespoon at a time. Once incorporated, continue beating until the whites are glossy and stiff peaks form, 8-10 minutes.
5. Fold in the pistachio mixture. Spoon the meringue onto a baking sheet covered with parchment paper. Spread into a 10-inch round and use the back of the spoon to make a slight indentation in the center.
6. Lower the preheated oven to 225° F and bake for 1 1/2 hours. Turn the oven off and, without opening, let the meringue rest in the oven for 1 hour. Transfer to a rack and let cool. Will keep in an airtight container or bag overnight.

Make the Rhubarb Curd:

1. Place the rhubarb, 1/4 cup superfine sugar, water, and rose water extract in a saucepan. Cover and cook over low heat, stirring occasionally, for 10 minutes or until rhubarb is completely softened. Blend with a hand mixer.
2. Place an inch of water in a medium saucepan and bring to a boil. Place the rhubarb mixture in a heatproof bowl. Add the egg yolks, butter, lemon juice and remaining 1/2 cup of sugar and whisk to combine. Place the bowl over simmering water and cook for 5 minutes, until mixture is smooth and thick.
3. Set aside to cool to room temperature, before serving. Will also keep in the fridge, covered with plastic wrap, for 2-3 days prior to use.

Make the homemade whipped cream:

1. Beat the heavy cream and sugar on medium high until soft peaks form.

Assemble the pistachio pavlova with rhubarb curd:

1. Spread whipped cream (optional) on pavlova, followed by rhubarb curd. If the mixture has gotten too thick from being chilled, add a splash of rosewater or lemon juice. Sprinkle with chopped pistachios and dried rose petals. Slice and serve immediately