In small saucepan, melt chocolate and butter in water over low heat; cool. In large mixer bowl, combine next 5 ingredients. Add 2 eggs, sour cream, vanilla and almond extract. On low speed, blend in chocolate mixture until smooth, about 1 minute. In small bowl, beat 1 egg, Mascarpone cheese and sugar until smooth. Spread chocolate batter in bottom of greased and floured 10x15-inch jelly roll pan. Drop cheese mixture by tablespoons over chocolate batter. Using a knife, gently swirl each several times to create a marble effect. Bake in preheated 375 F oven until wooden pick inserted in center comes out clean (about 25 minutes). Cool on wire rack. Cut into bars. In small microwavable bowl, microwave chocolate bar (medium) for 2 minutes, stirring once. Drizzle with chocolate. Serve at room temperature. Store covered in refrigerator.