Preheat oven to 300 F. Combine the vinegar, rosewater extract and corn starch in a bowl and set aside. Separate the egg whites from the yolks into a mixing bowl and make sure there are no droplets of yolks or any grease coming into contact with the egg whites. You will have trouble whipping the egg whites later. Beat the egg whites until they are foamy and white using a mixer (stand mixer is best if you have one). Gradually add in the sugar 1 tablespoon at a time and continue to beat until the meringue is glossy and forms a medium peak when you hold it up. Fold in the rosewater mixture until combined, but don't overmix it
You can drop the meringue onto the parchment-lined baking sheets using spoons to form a roughly 3-inch circle and about 1-inch apart from each other. Use the back of the spoon to create indentation in the middle. If you choose to use piping bag (which I did), spoon the meringue into the bag. Do not fill it up too much and snip the end of the piping back to create this 1-inch hole. Gently pipe out the meringue to form a roughly 3-inch circle and about 1-inch apart from each other. Use the back of the spoon to create indentation in the middle.
Lower the oven temperature to 215 degrees and pop the meringue into the oven. I baked both trays at the same time. One on top and one at the bottom. Bake for the next 1 hour 15 minutes. Turn off the oven and then leave the Pavlova inside the oven for another 1 hour. Remove from the oven to cooling rack to let them cool down completely
While the pavlova is baking, prepare the compote:
Place all the ingredients of the compote in a small saucepan and stir to mix everything. Make sure the cornstarch is dissolved. Place on stove top and bring to a gentle boil and let it simmer away until you can easily mashed the blueberries and the compote is thick. It will thicken further as it cools down. Let it cool down completely before using
Assembling:
Spoon about 1 Tablespoon or so of the compote on top of the pavlova followed by Great Grains Blueberry Morning cereal.
I recommend to top the pavlova with the compote and Blueberry morning cereal as many as you want to eat so the pavlova won't get soggy.