Preheat oven to 350 degrees F.
In a mixer, begin to whip the egg whites with cream of tartar, if using.. Slowly add the sugar. Whip the whites until stiff peaks.
Combine flour and confectioners' sugar (and nut powder if using), then fold into whites.
Load batter into pastry bag (use open star or any desired shape IF NOT using nut powder otherwise use no tip), and pipe quarter size meringues onto grease free parchment paper. Bake for 5 to 7 minutes until browned. Remove and cool before use.
Pipe buttercream from cake assembly into some of the meringues for a surprise.
Apply meringues to the cake after applying a heavy crumb coat. Cover completely. Put fresh berries or dollops of cooled, piped chocolate ganache between any gaps of the meringues.