In a saucepan, melt chocolate and butter over low heat, stirring frequently. Set aside. In a bowl, beat the eggs. Gradually add sugar, beating until thick. Combine flour, baking powder and salt; add to egg mixture. Stir in melted chocolate, extracts and nuts. Pour half of the batter into a greased 20 cm square baking pan; set aside. For filling, beat butter and cream cheese in a mixing bowl until light. Gradually add sugar, beating until fluffy. Blend in egg, flour and vanilla; mix well. Spread over batter in pan. Dollop remaining batter over filling. With a knife, cut through batter to create a marbled effect. Bake at 180ºC or 35-40 minutes or until brownies test done. Cool. Store in the refrigerator.