1. Line four 1/2-cup or one 2-cup heart-shaped mold with cheesecloth. Place molds in jelly-roll pan; set aside.
2. Beat 2/3 cup of the heavy cream in small mixer bowl on medium-high speed to soft peaks; set aside. Combine mascarpone cheese and sugar in large mixer bowl. Beat on medium-high speed until smooth. Add vanilla, lemon juice, and liqueur; beat just until combined. Gently fold in whipped cream. Spoon mixture evenly into prepared molds. Cover with plastic wrap and refrigerate overnight.Make Raspberry Sauce::
3. Meanwhile, puree raspberries in blender. Strain through fine sieve. Stir in lemon juice and liqueur. (Can be made ahead. Cover with plastic wrap and refrigerate overnight.) Makes 1-1/2 cups.
4. Invert molds onto center of 2 large serving plates, remove cheesecloth; pour enough Raspberry Sauce around each heart to cover bottoms of plates. Spoon remaining 2 tablespoons cream by 1/2 teaspoonfuls onto sauce and draw a toothpick through each to form hearts. Garnish with raspberries, if desired. Makes 4 servings.