Line a 9- x 5-inch loaf pan with plastic wrap. Set aside.
Melt chocolate, butter, and 1/2 cup corn syrup in a heavy saucepan over medium-low heat, stirring until smooth. Whisk together 1/2 cup whipping cream and egg yolks in a small bowl. Gradually stir into chocolate mixture, whisking constantly. Cook over medium-low heat 11 minutes or until mixture reaches 160°. Remove from heat, and let cool 45 minutes or until mixture reaches room temperature.
Beat remaining 1 1/2 cups whipping cream, powdered sugar, and vanilla extract at high speed with an electric mixer until soft peaks form. Gently fold into chocolate mixture until no white streaks remain. Pour chocolate mixture into prepared pan. Cover and freeze 3 hours or until firm.
Process raspberries and 1/3 cup corn syrup in a blender until smooth, stopping to scrape down sides. Pour raspberry mixture through a wire-mesh strainer into a 2-cup glass measuring cup, discarding seeds. Cover and chill until ready to serve.
Gently invert loaf pan onto a serving platter; remove pan and plastic wrap. Slice chocolate loaf into 12 servings, and serve with raspberry sauce.