For the cookie
1 1/4 cups plus 1 teaspoon confectioners’ sugar
1 cup (4 ounces) finely ground, blanched almonds
6 tablespoons egg whites (from about 3 extra-large eggs)
Pinch of salt
1/4 cup granulated sugar
For the filling:
3 large egg whites
1 cup sugar
1 cup (2 sticks) margarine, at room temperature, cut into pieces
To make the macaroons:
Preheat the oven to 350 degrees. In a medium bowl, stir together confectioners' sugar and ground almonds. In the bowl of an electric mixer fitted with the whisk attachment, whip egg whites with salt on medium speed until foamy. Increase speed to high and gradually add granulated sugar. Continue to whip until stiff glossy peaks form. With a rubber spatula, gently fold in the confectioners' sugar mixture until completely incorporated.
Line 2 baking sheets with silpats or parchment paper; set aside. Fit a pastry bag with a 3/8-inch #4 round tip, and fill with batter. Pipe 1-inch disks onto prepared baking sheets, leaving 2 inches between cookies. The batter will spread a little. Let stand at room temperature until dry, and a soft skin forms on the tops of the macaroons and the shiny surface turns dull, about 15 minutes.
Bake, with the door of the oven slightly ajar, until the surface of the macaroons is completely dry, about 15 minutes. Remove baking sheet from oven and let the macaroons cool completely on the baking sheet. Gently peel off the pan liner. Their tops are easily crushed, so take care when removing the macaroons. Use immediately or store in an airtight container, refrigerated for up to 2 days or frozen for up to 1 month.
Prepare the filling:
In a medium-sized bowl, whisk egg whites and sugar. Set the bowl over a pot of simmering water to form a double boiler. Heat mixture, whisking often, until it feels warm to the touch and sugar is dissolved, 3 to 5 minutes.
Transfer bowl to the mixer, and fit with the whisk attachment. Whip on high speed until mixture is stiff and shiny, 3 to 5 minutes. Add margarine, one piece at a time, and continue mixing until thoroughly incorporated. The filling can be kept, covered and refrigerated, up to 1 week. Bring to room temperature before stirring.
Fill a pastry bag with the filling. Turn macaroons so their flat bottoms face up. On half of them, pipe about 1 teaspoon filling. Sandwich these with the remaining macaroons, flat-side down, pressing slightly to spread the filling to the edges. Refrigerate until firm, about 1 hour.
To make coffee-flavored, mocha-colored macaroons: Add 2 drops brown food coloring to the egg whites after they are whipped and blend 1 1/2 teaspoons instant coffee dissolved in 1/2 teaspoon warm water into 1/2 cup macaroon filling.
To make raspberry-flavored macaroons: Add 2 drops pink food coloring to the egg whites after they are whipped. Add 1/3 cup good-quality raspberry jam to the filling.
You can use your imagination to create other colors and flavors to match your décor or theme.