Carefully separate egg whites from yolks, making sure there isn’t any yolk contaminating the whites. You can refrigerate the yolks in a sealed container for another use. Add the egg whites to a clean, dry bowl of a stand mixer with the whisk attachment, and start the mixer on medium speed for about 10-15 minutes, until soft peaks form.
Lower the speed and slowly add the sugar, one tablespoon at a time, until the sugar is no longer visible. Don’t rush this part. You’ll want to carefully scrape down the sides of the bowl halfway through. This part can take another 15 minutes or so.
Preheat the oven to 300 F. Line a baking sheet with a piece of parchment paper and draw an 8-inch circle on the centre of the paper.
When the sugar is all incorporated into the egg whites, increase the speed to medium-high and beat until the mixture is glossy and very stiff. This will take another 15 minutes or so.
Meanwhile, in a small cup, mix together the cornstarch and vinegar. When the egg whites are ready, pour in the cornstarch mixture and half of the lemon zest and beat on medium-high for about a minute.
Use a clean spatula to quickly scoop the meringue in the centre of the parchment circle, shaping it initially with straight sides and a flat top. Use the spatula to swipe upwards along the sides to create creases in the side and then swirl the top to finish. At this point, the pavlova should have soft, round edges.
Transfer to the centre rack of the preheated oven, and immediately turn the temperature down to 225 F. Bake for 90 minutes. Don’t open the door during the bake time! It will be tempting….don’t do it!
To make the saskatoon syrup, add 2 cups of saskatoons to a small saucepan with 2 cups of water over medium heat. Bring to a boil, and then turn down the heat to low and allow to simmer for about 10 minutes, stirring once and awhile until the fruit is broken down, and some of the water has evaporated.
Add the other half of the lemon zest from your pavlova to the saucepan. Pour the mixture into a sieve over a measuring cup, pressing the liquid into the measuring cup. Be patient! Press until you have every last drop. Pour the liquid back into the saucepan and simmer on low, stirring constantly until syrup thickens slightly. It will also thicken as it cools. Set aside until ready to assemble the pavlova. If it gets too thick, add water, a teaspoon at a time to thin it.
After the timer goes off for the pavlova, turn off the heat and crack the door of the oven slightly, allowing the pavlova to cool completely before removing it from the oven.
Just before serving, whip the cream until soft peaks form. Slice the vanilla bean down the middle vertically and scrape out the inside. Add it to the cream and gently fold in.
Spread the whipped cream on the top of the meringue, drizzle with saskatoon syrup and top with plums and more saskatoons. Slice and serve!