Poached rhubarb and raspberries float on a cloud of crisp meringue in this special dessert. Spread over an overturned mixing bowl, the meringue is left overnight in a barely warm oven to dry out.
Preheat oven to 200 degrees. Invert a 9-inch metal bowl on a work surface. Cut an 18-inch-square sheet of aluminum foil, and place over bowl, shiny side out. Using the plastic handle of a vegetable peeler or rubber spatula, smooth the foil against the bowl, eliminating any creases; set bowl aside. Fill a medium saucepan 1/4 full with water. Set the saucepan over medium heat, and bring water to a simmer.
Combine egg whites, 1/2 cup sugar, and cream of tartar in the bowl of an electric mixer. Holding the bowl over the simmering water, whisk constantly until sugar has dissolved and whites are warm to the touch, 3 to 4 minutes.
Transfer bowl to mixer. Start beating on low speed; gradually increase speed to high until stiff, glossy peaks form, about 10 minutes. Add vanilla extract; mix until combined.
Spoon the meringue over the foil on the inverted bowl. Using an offset spatula or a large spoon, gently spread the meringue to make a shell that is 1/2 to 1 inch thick and 2 inches deep. Without going over the rim of the bowl, make decorative swirls around the rim. Coat what will be the base of shell evenly so that it is flat; avoid making thin spots.
Place bowl, still inverted, on a baking sheet. Transfer to oven, and bake 25 minutes. Watch carefully; if the shell begins to brown, open oven door and lower temperature to 175 degrees. Bake 2 hours more at 175 degrees. Turn off heat, and leave the bowl in theÂ oven 12 hours or overnight to dry completely.
In a large bowl, prepare an ice bath. Combine 1 cup water, remaining 3/4 cup sugar, and kirsch, if using, in a small saucepan; bring to a boil. Add rhubarb chunks. Reduce heat to medium low; simmer until rhubarb is tender, about 6 minutes. Remove from heat. Transfer rhubarb to an empty bowl set over an ice bath; let cool completely. Chill until ready to use.
To assemble the dessert, place the bowl of an electric mixer and the whisk attachment in the freezer to chill, and have ice bath ready. Drain rhubarb through a strainer set over a bowl, reserving both the syrup and the rhubarb. Transfer syrup to a small saucepan. Set saucepan over medium heat; reduce by half or until syrup coats the back of a wooden spoon, 5 to 7 minutes. Transfer syrup to a bowl set over the ice bath; let cool completely.
Pour heavy cream into the chilled mixer bowl. Split vanilla bean lengthwise. Scrape out the seeds, and add to cream. Discard the pod. Beat on high speed until stiff peaks form.
Unwrap aluminum-foil edges from bowl, and slide bowl out of meringue shell. Turn shell right side up. Gently pull foil away from meringue, starting at rim and working toward the bottom, until shell is free.
Place meringue shell on a cake stand or plate. Spoon whipped cream into shell. If shell breaks, press it back together. Spoon rhubarb chunks over whipped cream, and garnish with raspberries. Serve any remaining rhubarb syrup on the side. Dust with confectioners' sugar. Using a pie server or spoon, serve immediately.
This dessert can be prepared one day ahead by following steps 1 through 6 and storing the poached rhubarb in an airtight container in the refrigerator.