Place a piece of parchment paper on a baking sheet and draw a 9-inch circle using a plate as a template. Flip the parchment paper over and set aside.
Preheat oven to 300˚F.
In the bowl of a stand mixer, beat egg whites until stiff peaks. Slowly stream in the sugar while mixing. Beat until thick and glossy. Add the lemon juice, vanilla, and corn starch and gently fold in. Spread mixture onto the parchment paper, spreading it evenly to the edge of the drawn circle.
Bake for 60 minutes. Cool completely on a wire rack and then place on a platter and add toppings.
For the Toppings
Beat the whipping cream with sugar until soft peaks.
Spread over cooled pavlova and then top with berries and a few mint leaves. Slice and serve.