Heat oven to 200 degrees. Line a baking sheet with parchment paper. Brush with 1 tablespoon butter; coat with flour. Set aside.Advertisement
Whisk together the almonds, 1/4 cup superfine sugar, and the confectioners' sugar; set aside. In the bowl of an electric mixer fitted with the whisk attachment, beat the egg whites until they form soft peaks. One tablespoon at a time, slowly add remaining 1/4 cup superfine sugar; continue to beat until mixture forms stiff peaks. Fold in the nut mixture. Spread the mixture onto the prepared baking sheet until it is 1/4 inch thick.
Bake the dacquoise 2 hours; then turn off the oven, and leave inside until completely cooled, about 30 minutes.
Using a serrated knife, carefully cut dacquoise into three 4-by-7-inch pieces. Wrap each piece individually in plastic wrap, and set aside. Save the leftover dacquoise for another use. The dacquoise can be made several days in advance and stored in an airtight container in a cool, dry place.