Beat butter at medium speed with an electric mixer until soft and creamy; gradually add sugar, beating well. Add eggs and chocolate, mixing well. Add flour to butter mixture, mixing well; stir in walnuts.
Spoon half of batter into a greased and floured 9-inch square pan. Spread raspberry jam over batter; top with remaining batter.
Bake mixture at 350 degrees F. for about 28 to 30 minutes.