Special equipment: Oven with
convection setting, 4 baking sheets, 3 silicone baking mats, Fine-mesh
sieve, Pastry bag with 1/4-inch round tip
Preheat the oven to 300 degrees F using the convection
setting. Line 3 baking sheets with silicone mats. Measure the
confectioners' sugar and almond flour by spooning them into measuring
cups and leveling with a knife. Transfer to a bowl; whisk to combine.
Sift the sugar-almond flour mixture, a little at a time,
through a fine-mesh sieve into a large bowl, pressing with a rubber
spatula to pass through as much as possible. It will take a while, and
up to 2 tablespoons of coarse almond flour may be left; just toss it.
Beat the egg whites, cream of tartar and salt with a mixer
on medium speed until frothy. Increase the speed to medium high;
gradually add the superfine sugar and beat until stiff and shiny, about 5
more minutes.
Transfer the beaten egg whites to the bowl with the almond
flour mixture. Draw a rubber spatula halfway through the mixture and
fold until incorporated, giving the bowl a quarter turn with each fold.
Add the food coloring and extract (see below). Continue
folding and turning, scraping down the bowl, until the batter is smooth
and falls off the spatula in a thin flat ribbon, 2 to 3 minutes.
Transfer the batter to a pastry bag fitted with a 1/4-inch
round tip. Holding the bag vertically and close to the baking sheet,
pipe 1 1/4-inch circles (24 per sheet). Firmly tap the baking sheets
twice against the counter to release any air bubbles.
Let the cookies sit at room temperature until the tops are
no longer sticky to the touch, 15 minutes to 1 hour, depending on the
humidity. Slip another baking sheet under the first batch (a double
baking sheet protects the cookies from the heat).
Bake the first batch until the cookies are shiny and rise
1/8 inch to form a "foot," about 20 minutes. Transfer to a rack to cool
completely. Repeat, using a double sheet for each batch. Peel the
cookies off the mats and sandwich with a thin layer of filling (see
below).
Almond-Raspberry:
Tint the batter with 2 drops neon pink gel food coloring;
flavor with almond extract. Fill with seedless raspberry jam (you'll
need about 3/4 cup).
Mint-White Chocolate:
Tint the batter with 2 drops mint green gel food coloring;
flavor with mint extract. For the filling, microwave 3 ounces chopped
white chocolate, 2 tablespoons heavy cream and 1 tablespoon butter in
30-second intervals, stirring, until smooth. Stir in 1/4 teaspoon mint
extract and 1 drop mint green gel food coloring.
Blueberry Cheesecake:
Tint the batter with 3 drops royal blue gel food coloring;
flavor with vanilla extract. For the filling, mix 4 ounces softened
cream cheese and 3 tablespoons blueberry jam.
Lavender-Honey:
Tint the batter with 2 drops violet gel food coloring;
flavor with almond or vanilla extract. For the filling, mix 3/4 cup
mascarpone cheese, 2 tablespoons honey and 1 teaspoon ground dried
lavender.
Pineapple:
Tint the batter with 2 drops lemon yellow gel food
coloring; flavor with vanilla extract. For the filling, press 3/4 cup
pineapple jam through a sieve, discarding any large pieces.
