Step 1: Place eight 2 1/2-inch diameter-by-3-inch-tall pastry ring molds on a parchment paper lined baking sheet; set aside.
Step 2: In the bowl of a stand mixer fitted with a whisk attachment on medium high speed, whip 1 pound mascarpone cheese, 1/2 cup sugar, 2 tablespoons Limoncello liqueur and the zest of one lemon until creamy, about 10 minutes. Add 1 cup heavy cream and whip until soft peaks form, about 3 to 4 minutes.
Step 3: Using a pastry bag or spoon, divide mousse mixture between ring molds and freeze several hours or until firm.
Step 4: To unmold, place 8 sugar cookies on a baking sheet. Using a paring knife, run the knife around the inside of the ring mold to loosen the mousse. Place mold on top of cookie and press the frozen mousse onto sugar cookie. Refrigerate 2 hours.
Step 5: To serve, use a spatula to transfer sugar cookie topped with mousse to a serving plate. Break another sugar cookie in half and press the half cookie into the top of the mousse. Top with a sprig of fresh mint. Garnish plates with raspberry sauce, lemon curd and a chocolate straw, if desired.
