Step 1

Place egg whites in a large mixing bowl and let stand at room temperature for 30 minutes. Line two large cookie sheets with parchment paper; set aside.

Step 2

Place the almond flour and powdered sugar in the bowl of a food processor. Cover and process for 1 minute, stopping once to scrape up the flour mixture from the bottom of the bowl. Sift the almond flour mixture, a little at a time, through a medium-mesh sieve into a medium bowl, pressing with the back of a spoon to pass through as much as possible. Discard any coarse almond flour that may be left in the sieve (up to 1 tablespoon).

Step 3

Add the cream of tartar to the egg whites. Beat with an electric mixer on medium speed until frothy, about 1 minute. Gradually add the granulated sugar and beat on high speed until stiff and shiny, about 4 more minutes.

Step 4

Gently add the flour mixture to the egg whites. Fold the flour mixture into the egg whites by gently drawing a rubber spatula halfway through the mixture and fold until all flour mixture is incorporated, giving the bowl a quarter turn with each fold (about 50 strokes). Add the almond extract. Continue folding and turning, scraping down the bowl, until the batter is smooth and falls off the spatula in a thin flat ribbon, about 2 to 3 minutes. (You should have about 1 1/2 cups batter.)

Step 5

Transfer the mixture (batter will be thin) to a large decorating bag fitted with a large (about 1/4-inch) round tip. Pipe 1 1/4-inch circles 1 inch apart onto the prepared cookie sheets. Firmly tap the baking sheets five to eight times against the counter to release any air bubbles. Let stand for 30 to 45 minutes or until the tops of the cookies are no longer sticky to the touch.

Step 6

Preheat oven to 300°F. Bake about 18 minutes or until tops of cookies are set, shiny and rise 1/8-inch to form a "foot". Cool completely on cookie sheets on a wire rack. Carefully peel cookies off parchment paper.

Step 7

Spread Almond Butter Frosting onto bottoms of half of the cookies. Top with the remaining cookies, bottom sides down.