In a large mixing bowl, beat the butter, eggs, and sugar until the sugar is dissolved. Add the vanilla and lemon extract, cream cheese, and sour cream. Mix until smooth. Add the flour and baking powder. Mix well.
Pour the batter into a greased 10 1/4 in. spring form.
Bake at 325° until the top is golden brown. This will take from 75 to 90 minutes.
You can serve it whenever you like, but it's better if you let it cool to room temperature.