Heat oven to 350° F. Using an electric mixer fitted with a whisk attachment, beat the egg whites on high until stiff peaks form, about 1 1/2 minutes. With the mixer running, slowly add the granulated sugar. Continue beating until glossy, about 1 minute. Add the orange zest and vanilla. In a small bowl, combine the flour and baking powder. Gently fold the flour mixture into the egg mixture until no white streaks remain. Spoon the batter into a large resealable plastic bag. Using scissors, cut the end off a corner of the bag to create a circle about 1/2 inch in diameter. On a parchment-lined baking sheet, pipe the batter into 24 1 1/2-inch rounds (about the size of silver dollars). Bake until puffed and golden, about 12 minutes. Transfer to a rack to cool completely. Meanwhile, in a small bowl, combine the sour cream and preserves. Spread some of the raspberry mixture onto the bottom of half the cookies. Form sandwiches with the remaining cookies. Sprinkle with the confectioners' sugar just before serving.
Tip: If there's no time to bake, sandwich the berry-cream filling between store-bought cookies.