Preheat oven to 225°.
In a large bowl, with a mixer (preferably fitted with wire-whisk attachment) on high speed, beat egg whites and cream of tartar until foamy. Gradually add 1 cup sugar, about 1 tablespoon at a time, beating well after each addition and scraping sides of bowl occasionally, until stiff, shiny peaks form (see tip 2 below).
Line two 12- by 15-inch baking sheets with cooking parchment or coat sheets with cooking-oil spray or butter. Mound meringue in eight equal portions (a scant 1/2 cup for each) on sheets, spacing at least 3 inches apart. Shape each into a 4-inch round (follow tip 3 below).
Bake in preheated oven until meringues sound hollow when tapped and feel firm to the touch, about 1 1/2 hours (1 1/4 hours in convection heat); switch sheet positions halfway through baking. Turn heat off and leave meringues in closed oven until completely cool, 2 to 2 1/2 hours longer. Remove from sheets.
Shortly before serving, rinse and drain berries; pat dry with a towel. In a bowl, with a mixer on high speed, beat whipping cream just until soft peaks form. Turn mixer to low and beat in sugar to taste (about 2 tablespoons).
Set meringues on dessert plates. Top with whipped cream and berries.
Tips for the perfect meringue
A wire-whisk attachment introduces air evenly into whites and creates small bubbles, which are both stronger and more flexible. Make sure the bowl and beaters are clean; any fat can interfere with the formation of the foam.
Beating the whites with an acid, like cream of tartar or vinegar, helps coagulate the egg-white protein. You want stiff, shiny peaks. The mixture should feel smooth when you rub it between your fingers.
Shape meringue mixture into bowl-shaped rounds with a small, thin spatula. The edges should be a little higher than the centers.