Crazy delicious vegan and gluten free dessert! Make the meringues first. You can also roast the rhubarb the day ahead. Just before serving stir the strawberries into the rhubarb compote. The compote is enough for 6 to 8 servings. Vegan meringue recipe makes about 16 meringue nests. Egg white meringue recipe makes about 11 nests.
Preheat oven to 200°F. Line 2 large baking sheets with parchment. With an electric mixer or stand mixer with whisk, whip the egg whites with the cream of tartar until foamy. Add the cream of tartar and continue to beat until soft peaks form. Gradually sprinkle in the sugar, whipping until the whites form glossy, stiff peaks, 3 to 5 minutes. Be careful not to overbeat. Make a slurry with the arrowroot, vinegar, and vanilla. Add to the meringue and whip until incorporated.
Scoop 1/3 cup mounds onto the parchment-covered baking sheet. (I use a #16 cookie scoop.) Use the back of a spoon to hollow out the centers. If you are comfortable with a pastry bag, you can pipe the meringue through a large star-shaped tip, and form nests—higher on the edges than the center.
Bake about 2 hours, until the meringue is dry. (see note)