Place 12 paper or foil cupcake liners into 12 standard-size muffin-pan cups. Press shortbread cookies, flat side up, in bottoms of each lined cupcake cup (they should fit snugly).
In small bowl, stir together 2 tablespoons liqueur and 2 tablespoons water. Pour 1 teaspoon of thinned amaretto mixture over each cookie.
In medium-size bowl, on low speed, beat remaining 3 tablespoons liqueur and mascarpone just until blended. Gradually beat in 7 tablespoons water until smooth. Sprinkle mousse mix over top. Beat on low speed 1 minute; increase speed to medium-high and beat until thick and lightened in color, 2 to 3 minutes. Transfer mixture to large pastry bag or plastic food-storage bag fitted with large star tip. Pipe mousse into cookie-lined cups. (Or, spoon 2 slightly rounded tablespoons into each cup.) Refrigerate at least 1 hour to firm.
In small skillet, toast almonds over medium-high heat until golden, 3 minutes. Transfer to small bowl.
Garnish mousse with toasted almonds just before serving.