Preheat the oven to 200 degrees with two racks centered. Trace a 9-inch circle on each of 2 pieces of parchment paper. Turn over, and use each piece to line a baking sheet. Set aside.
Place egg whites in the clean bowl (copper, if possible) of an electric mixer fitted with the whisk attachment. Beat on high speed until soft peaks form, about 2 minutes. Add 1/4 cup granulated sugar; beat to combine. Gradually add remaining 1 1/4 cups granulated sugar, 1 tablespoon at a time, until whites are very stiff and glossy. Add 1 teaspoon vanilla; beat just until combined.
Divide batter between the traced circles, and use an icing spatula or rubber spatula to spread evenly to the edges of the circles.
Place baking sheets on separate racks in the oven, and bake about 3 1/2 hours, switching the upper and lower sheets every 30 minutes. When fully cooked, the meringues should be white and dried and crisp on the outside, yet soft and somewhat chewy inside; test by tapping the center lightly with a fork. Remove from oven, and let cool completely on baking sheets.
Combine cream, remaining 1 teaspoon vanilla and 2 tablespoons confectioners' sugar in a chilled metal bowl; whip until cream is stiff but soft.
Place one meringue on a serving plate, and spread 3/4 of the whipped cream over it. Scatter half of the berries over, and place the second meringue on top. Spoon remaining cream onto the center of the meringue, and heap remaining berries on top. Dust the top with confectioners' sugar.
Slice the vacherin with a thin sharp knife, and serve immediately with red raspberry sauce on the side.