Line two baking sheets with parchment paper; set aside. In large mixing bowl beat butter on medium to high 30 seconds. Add sugars; beat until well-combined. Beat in cocoa, baking soda, and salt. Add vanilla. Beat in egg. Beat in as much flour as you can; stir in remaining by hand.
Divide dough in three portions. Shape each portion in 8-inch log about 1-1/2 inches in diameter. (For small cookies shape dough in 9-inch logs about 1 inch in diameter.) Wrap in plastic wrap or waxed paper. Freeze 2 to 3 hours or until firm enough to slice.
Heat oven to 350 degrees F. Cut logs in 1/4-inch slices. Place 1 inch apart on prepared baking sheets. Bake 8 to 12 minutes or until edges are firm. Cool 1 to 2 minutes on baking sheets. Transfer to wire racks; cool completely.
Spread the flat side of half the large cookies with 2 teaspoons Raspberry Filling (use 1 teaspoon filling for small cookies). Top with remaining cookies. Makes 30 large/38 small sandwiches.
In small saucepan melt white chocolate over medium-low heat; cool. Meanwhile, in large mixing bowl beat butter until creamy. Beat in raspberry preserves and vanilla. Gradually beat in powdered sugar and cooled white chocolate. Add whipping cream until spreadable.