Pavlovas: Put an oven rack in the center of the oven. Preheat the oven to 200 degrees F. Line a baking sheet with parchment paper. Set aside.
In a stand mixer fitted with the whisk attachment, beat the egg whites until thick, about 2 minutes. With the machine on medium-high speed, gradually add the sugar, about 1 tablespoon at a time. Add the salt, cream of tartar and lemon zest. Increase the speed to high and beat until the mixture holds stiff peaks, about 3 to 4 minutes. Drop 8 (1/2) cupfuls of the mixture onto the prepared baking sheet about 2 inches apart. Using the back of a spoon make a 1 1/2-inch diameter well in the center of each meringue. Bake for 2 hours. Turn off the oven and allow the meringues to cool completely in the oven for 2 hours. Store airtight in a plastic container for up to 1 week.
Berries: In a small bowl, toss together the berries, sugar and lemon juice. Refrigerate for at least 1 hour.
Cream: In a small bowl, mix together the cheese, sugar and vanilla until smooth.
Assembly: Put the meringues on small plates and spoon a dollop of the mascarpone cream into the wells. Top with the berries and serve.
Cook's Note: If using blueberries, gently mash them with a fork before mixing with the sugar and lemon juice.
Cook's Note: The meringue mixture can also be placed in a pastry bag fitted with a large, plain tip (recommended: Ateco # 9808) and piped onto the baking sheet.