Elegant cookies with a crisp exterior and chewy center and found in pastry shops throughout Paris.
Preheat oven to 300 degrees.
Sift powdered sugar in a bowl. Whisk in almond flour and set aside.
Line two parchment paper and draw out circles using a 1-1/2 cookie cutter dipped in flour.
Whip the egg whites with an electric mixer on medium speed. Gradually add in the sugar, 1 teaspoon at a time, until it reach medium soft peaks.
Using a rubber spatula, gently fold in half of the flour mixture into the egg whites until just incorporated.
Add in the vanilla and the remaining flour until just combined without deflating the batter. Tap bowl on counter to eliminate any air pockets.
Transfer mixture to a piping bag. Using a piping bag with a 1/2 inch plain tip, pipe out mixture into small circles on prepared parchment.
Bake for 20 to 25 minutes, rotating pan halfway between, until macaroons feel slightly firm to the touch and can be gently lifted off parchment.
Let cool on baking sheet for 5 minutes before transferring parchment to a wire rack to completely cool.
Using an offset spatula, remove macaroons and spread 2 teaspoons of buttercream on flat sides of half the macaroons; sandwich with the other halves.
Refrigerate until firm, about 20 minutes before serving.
Mix together the softened butter, shortening and powdered sugar and vanilla.