Preheat the oven to 300F. Grease and lightly flour a 9 3/4 in tube pan. Shake out any excess flour from the pan. With a mixer or by hand, blend the butter and sugar together in a large bowl;beat until the mixture is light and fluffy. Gradually add the eggs and lemon extract, and beat well. Sift the flour and baking powder together three times; add the nuts and raisins. Gradually add the dry ingredients to the creamed mixture and blend well. Pour the batter into the tube pan. Bake 1 1/2 to 2 hours, or until a cake tester comes out clean. Cool the cake for 15 minutes, then remove it from the pan. Serve it dusted with powdered sugar, if desired.