6 oz sliced blanched almonds (not slivered; 2 cups)
1 1/2 cups confectioners sugar
3 large egg whites
3/4 teaspoon salt
3 tablespoons granulated sugar
For chocolate raspberry ganache
3 oz fine-quality bittersweet chocolate (60 to 64% cacao), finely chopped
1/3 cup heavy cream
1 tablespoon unsalted butter, softened
1/16 teaspoon raspberry extract (preferably McCormick brand)
Special equipment: parchment paper; a gallon-size sealable plastic bag (not pleated)
Line 2 baking sheets with parchment paper.
Pulse almonds with 1/2 cup confectioners sugar in a food processor until very finely ground, 2 to 3 minutes, then transfer to a bowl. Sift in remaining cup confectioners sugar, stirring to combine.
Beat egg whites with salt in another bowl with an electric mixer at medium speed until they just hold soft peaks. Add granulated sugar, a little at a time, beating, then increase speed to high and continue to beat until whites just hold stiff, glossy peaks. Add drops of food coloring to reach desired shade and mix at low speed until evenly combined. Stir almond mixture into meringue with a rubber spatula until completely incorporated. (Meringue will deflate.)
Spoon batter into bag, pressing out excess air, and snip off 1 corner of plastic bag to create a 1/4-inch opening. Twist bag firmly just above batter, then pipe peaked mounds of batter (the size of a chocolate kiss) onto lined sheets about 1 1/2 inches apart. Let cookies stand, uncovered, at room temperature until tops are no longer sticky and a light crust forms, 20 to 30 minutes.
Meanwhile, put oven racks in upper and lower thirds of oven and preheat oven to 300°F.
Bake cookies, switching position of sheets halfway through baking, until crisp and edges are just slightly darker, 20 to 25 minutes. Cool completely on sheets on racks, about 30 minutes.
Make ganache while macaroons bake:
Melt chocolate with cream in a metal bowl set over a pan of barely simmering water or in top of a double boiler, stirring until smooth. (Bowl should not touch water.) Remove bowl from heat, then add butter and raspberry extract, stirring until butter is melted. Let stand at room temperature until cooled completely and slightly thickened.
Carefully peel cookies from parchment (they will be fragile). Sandwich a thin layer of ganache (about 1/2 teaspoon) between flat sides of cookies.