Make the Brown Sugar Meringues (up to 2 days ahead)

1. Preheat oven to 250F. Line a large baking sheet with parchment paper.
2. Using a mixer on medium speed, whisk the egg whites until soft peaks form. Increase speed to medium-high and slowly add in white and brown sugars, one spoonful at a time. Continue beating until sugar has been completely incorporated and the whites have been beaten into stiff peaks, gently fold in the vinegar, corn starch and vanilla.
3. Spoon the meringue into twelve large dollops onto the prepared cookie sheet.
4. Bake in preheated oven for 90 minutes, or until the surface of the meringues feels dry to the touch. Turn off the oven off and leave the meringues in the oven with the door closed to cool for at least an hour, or preferably overnight.
5. (If making ahead, transfer the cooled meringues to a paper-lined container with a tightly-fitting lid, and store in a cool, dark place)

Rhubarb Compote (can be made up to 1 week ahead)

1. In a medium heavy-bottomed saucepan set over medium-high heat, combine the rhubarb, orange juice, sugar and orange zest. Bring to a boil, stirring occasionally, the reduce heat to low and simmer for 10 minutes, or until rhubarb is soft and beginning to fall apart. Set aside to cool off to room temperature (if making in advance, store in an airtight container in the refrigerator until ready to use, or for up to 1 week).

Make the Yogurt Cream (shortly before assembling)

1. In a large mixing bowl, whip together the heavy cream, yogurt, sugar and vanilla until soft peaks form.

Assemble the Eton Mess (at the last possible minute)

1. Crumble meringues into a large mixing bowl. Top with alternating spoonfuls of yogurt cream and rhubarb compote, and fold until just barely combined - the mixture should still look quite streaky and, well, messy.
2. Divide evenly between six dessert bowls or martini glasses, and serve immediately.