Pavlova with Rhubarb and Pistachios

Preheat oven to 200 degrees. Stir together 1 cup sugar and the cornstarch in a small bowl. Beat together egg whites, 1 teaspoon lemon juice, and 1/4 teaspoon salt with a mixer on low speed until very frothy. Increase speed to medium-high and gradually add sugar mixture, beating until stiff, glossy peaks form, 12 to 15 minutes, scraping down sides of bowl halfway through.

Mound meringue onto a parchment-lined rimmed baking sheet and gently spread into a 7-inch circle, leaving a well 3 1/2 inches wide and 1 inch deep in the center. Bake until meringue is crisp on the outside and the texture of marshmallow on the inside, about 2 1/2 hours. (If meringue starts to brown, reduce oven temperature to 175 degrees.) Turn off heat and let meringue cool in oven at least 2 1/2 hours or up to overnight.

Preheat oven to 400 degrees. Combine rhubarb, water, remaining 3/4 cup sugar, remaining tablespoon lemon juice, and a pinch of salt in a 9-by-13-inch glass baking dish. Bake until just tender, 10 to 12 minutes, spooning juices over halfway through.

Carefully transfer rhubarb pieces (they will be very soft) to a parchment-lined rimmed baking sheet with a spatula; reserve juices. Let cool completely.

Just before serving, beat together cream and vanilla until soft peaks form. Place meringue on a serving platter and fill with whipped cream. Top with rhubarb, and garnish with pistachios. Spoon over pavlova and rhubarb juices, and serve immediately.