Preheat the oven to 250°F. Line two baking sheets with parchment paper and set aside. If desired, trace a large star shape on one of the parchments. Flip the paper over so the ink is on the bottom of the sheet. Otherwise you can pipe the star shape free handed.
Prepare a large piping bag fitted with a large star tip and set aside. To create small stars for garnish, fit 1 or 2 more pastry bags with smaller star tips of varying size and set aside.
Add the egg whites to the bowl of a stand mixer. Whip the egg whites on high speed with a whip attachment. When the egg whites begin to stiffen and create soft peaks, lower the speed and begin to slowly add the sugar. Add the sugar in several small increments.
Once the sugar has been added, turn the speed back up and continue beating the egg whites until the sugar has dissolved completely. Check that the sugar is dissolved by rubbing a little meringue between two fingers – it should feel completely smooth with no grains of sugar in it. If you still feel the sugar, continue to beat the meringue. This will take 5 to 8 minutes.
Meanwhile, combine the vanilla, vinegar, and cornstarch in a small bowl and stir. When the sugar has been fully dissolved into the egg whites, turn the speed down to low. Add the cornstarch mixture and then turn up the speed. Mix just until the cornstarch mixture is fully incorporated.
Add a small amount of the meringue to the piping bags with the small star tips, about ½ cup each. Pipe out small stars onto one of the parchment-lined baking sheets. Pipe as many as you would like for garnish, at least 20 to 30 if they are very small. You can do less if the stars are larger.
Transfer the remaining meringue to the large piping bag fitted with the large star tip. Begin by piping a circle in the middle of the second parchment-lined baking sheet. Pipe the 5 rays out evenly around the circle to make a large star shape. Pipe a raised border around the middle circle to create a small indent that can be filled with the topping later.
Bake the meringues for 1 hour. Check the baking sheet with the small stars after 45 minutes to check if they are down – they will cook much faster than the larger meringue. The small stars are done when they are dry to the touch.
After 1 hour, turn the oven off and leave the large meringue in the oven for another hour then remove and allow to cool completely.
Lemon Curd
Place a fine mesh strainer over a bowl and set aside. Cut the butter into small pieces and have it ready by the stove.
In a small saucepan combine the sugar and egg yolks. Add the lemon juice and whisk until completely combined. Place over medium heat. Bring to a simmer while stirring constantly. Allow the mixture to bubble a few times before removing from the heat.
Whisk the cold butter into the lemon mixture until it melts. Pour the mixture through the strainer into the bowl. Place a piece of cling film directly on top of the lemon mixture to prevent a skin from developing. Chill the curd until it is completely cold and has firmed up.
Blueberry Sauce
In a small saucepan combine the frozen blueberries and sugar. Place over medium high heat and bring the fruit to a boil. In a small cup combine the water and cornstarch. Add the cornstarch slurry to the boiling blueberries and stir quickly to combine. Once the mixture thickens, remove from the heat and stir in the lemon juice and salt.
Transfer the blueberry sauce to a bowl and place a piece of cling film directly on top of the blueberries to prevent a skin from developing. Chill until completely cold.
To Assemble
In the bowl of a stand mixer, add the whipping cream and sugar. Beat with a whip attachment until stiff peaks. Add the mascarpone and beat just until combined and the mixture has stiff peaks.
Before proceeding, ensure both the lemon curd and blueberry sauce are cold to prevent the cream from melting. Add ½ cup of the lemon curd and mix just until combined. Remove the bowl from the mixer. Add 2/3’s of the blueberry sauce and fold it gently together, leaving it marbled if desired.
Carefully remove the meringue from the parchment paper and place on a large serving platter.
Spoon the whipped mascarpone topping mixture in the centre of the pavlova as well as down the middle of each ray. Drizzle the remaining blueberry sauce decoratively over the top. Scatter the small stars over the pavlova and on the serving platter. Enjoy!