Preheat oven to 225°F and line a baking sheet with parchment paper, Pro Tip: Place a dab of the meringue on the baking sheet in each corner before lining with parchment. This will help it stay in place!.
In a completely clean mixing bowl, combine egg whites, cream of tartar, salt, and vanilla.
Beat on low speed, gradually increasing to high until foamy.
Slowly add the sugar one tablespoon at a time while continuing to beat.
Continue mixing until glossy, stiff peaks form and the sugar is fully dissolved.
Transfer to a piping bag fitted with a large round or star tip.
Pipe eight 4½- to 5-inch circles. Flatten the centers slightly, then pipe a raised border around each to create nests.
Bake for 75 minutes.
Turn the oven off and leave the door closed for 2 hours until completely cool.
In a bowl, toss the berries with lemon juice and optional sugar. Let sit for about 10 minutes if desired.
Beat heavy cream, powdered sugar, and vanilla until medium-stiff peaks form.
Top generously with fresh berries.
Garnish with fresh mint and whipped cream and serve immediately.