Preheat oven to 375 degrees. Spray mini-heart pan with vegetable spray. Dust with cocoa powder. In 2-quart saucepan, melt chocolate and butter over low heat, stirring constantly, until chocolate is melted. Stir in flour, sugar and vanilla. Stir in eggs until well-mixed. Stir in walnuts. Pour into prepared pan. Bake 20 to 25 minutes or until wooden pick inserted in center comes out clean. Cool in pan 5 minutes on wire rack. When cool pour chocolate glaze over cakes. Garnish with fresh raspberries and mint leaves, if desired. Serve chilled.
Glaze: Heat whipping cream just to boiling point. Don't boil. Add chocolate and stir until smooth and glossy. If mixture is too thin, wait a few minutes until it cools slightly and thickens. Put cooled cakes on wire rack over sheet of waxed paper. Pour glaze onto center of each cake and work toward edges.