Preheat oven to 180ºC F. Butter an 20 cm square pan. Melt chocolate and butter in medium sized heavy saucepan over low heat. Remove from heat; cool slightly. Stir in eggs, honey and vanilla. Combine flour, baking powder and salt in small bowl. Stir in chocolate mixture with walnuts. Spread batter evenly in prepared pan. Bake 20-25 minutes or just until center feels springy. Cool in pan on wire rack. Cut into 5 cm squares.