Preheat oven to 375°F. Butter and flour a 9~10" spring form pan.
Cream butter and sugar in a stand mixer or using a hand mixer until light and fluffy.
Add the eggs one at a time and beat until combined.
Slowly add the flour, salt, baking powder, vanilla extract (or lemon zest), grated apple and ricotta cheese. Beat until well combined.
Pour into the prepared pan and bake for 35~40 minutes or until the cake is golden brown and the sides start to pull away from the pan.
Cool in the pan for 10 minutes, then turn it out onto a wire rack rack and cool completely. Sift confectioners sugar over the top just before serving.