Step 1

Preheat the oven to 320 degrees F. Line 3 baking sheets with silicone mats or parchment. 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.

Step 2

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; save for another use.

Step 3

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.

Step 4

Transfer the beaten egg whites to the bowl with the almond flour mixture. Fold in the egg whites by drawing a rubber spatula halfway through the mixture and folding until incorporated, giving the bowl a quarter turn with each fold.

Step 5

Add the desired 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.

Step 6

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.

Step 7

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).

Step 8

Bake the first batch until the cookies are shiny and rise 1/8 inch to form a "foot," 12 to 14 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).

Step 9

Almond-Raspberry:

Step 10

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).

Step 11

Mint-White Chocolate:

Step 12

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.

Step 13

Blueberry Cheesecake:

Step 14

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.

Step 15

Lavender-Honey:

Step 16

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.

Step 17

Pineapple:

Step 18

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.