Strawberry-Rhubarb Rolled Pavlova

Pavlova: Preheat oven to 400°F. Brush a 9-by-12 1/2-inch rimmed baking sheet (quarter sheet pan) with butter. Line with parchment, leaving a 2-inch overhang on long sides; butter parchment. Whisk egg whites with salt on medium-high speed until soft peaks form, about 2 minutes.

Continue whisking, gradually adding granulated sugar, until fully combined and stiff, glossy peaks form, 7 to 9 minutes more. Beat in vanilla, then cornstarch and vinegar. Spread mixture evenly into prepared sheet.

Reduce oven temperature to 375°F and bake until pavlova puffs and collapses slightly, and turns golden brown and crisp on top, about 30 minutes. Remove from oven; let cool on sheet on a wire rack 5 minutes. Lightly dust top with confectioners' sugar. Turn out onto wire rack lined with a new piece of parchment, then peel off baked parchment and let cool 20 minutes more.

Filling: Spread jam evenly over pavlova, leaving a 1/2-inch border. Top with sliced strawberries in a single layer. Beat cream on medium-high speed to stiff peaks, then spread evenly over berries. Starting from one long end, roll up pavlova to form a tight log (lift with parchment from rack to make rolling easier), and place on a serving platter, seam-side down. If not serving immediately, refrigerate, wrapped in parchment, up to 1 day.