Preheat oven to 350°F (180°C). Line a large baking sheet with parchment paper. Trace an 8 inch cake or pie pan onto the middle of the paper. Flip the sheet over so the pencil mark is underneath.
Place six egg whites in a large bowl or stand mixer. Whip until egg starts to become foamy. Add sugar, 1 tablespoon at a time, until sugar is incorporated. Whip until stiff, shiny peaks form. Sprinkle in the cornstarch, lemon juice and zest. Gently fold in with a rubber spatula.
Mound meringue onto the circle drawn on the parchment. Smooth the top and sides with an offset or rubber spatula, using the circle as a guide. Place the baking sheet into the oven and immediately LOWER OVEN TEMPERATURE to 300°F (150°C). Bake for about 1 hour. Meringue should look dry but the center will be soft when poked. It's fine if cracks form. Turn off oven, leave door slightly open (prop open with a wooden spoon) and allow to cool completely in the oven.(* This step may be done the night before, leaving meringue in oven overnight.) Make the lemon curd. Place a large, heatproof bowl over a large pot with 2 inches of simmer water. Place all the ingredients for the lemon curd into the bowl. Whisk to combine. Continuing whisking until mixture thickens. Dip the back of a spoon into the curd and draw a line with your finger. If the line holds, the curd is ready.
Transfer to a small bowl. Lay a sheet of plastic wrap directly on top to prevent a skin forming. Allow to cool. (*If making ahead of time, store in refrigerator. Microwave briefly or heat in a saucepan over low to warm slightly and stir well before using.) Right before assembling, whip cream. Add the heavy cream to a bowl or stand mixer, along with the sugar and vanilla. Whip until soft, billowy peaks form.
To assemble, invert the meringue onto a serving plate. To do this, place your hand under the parchment paper, hold the plate on top of the meringue and gently flip. Peel the parchment off the meringue. It's fine if pieces fall off or more cracks appear.
Spread the lemon curd on top of the meringue. Mound on the whipped cream. Arrange the blueberries on top. Sprinkle the sliced almonds and scatter mint leaves and lemon zest over everything. Slice and serve.