Preheat the oven to 375 degrees
Grease an 8 inch round pan with butter.
In a large bowl using a spatula or hand held mixer mix the softened butter and sugar until creamy.
Add eggs and combine well.
Add the flour,baking powder and salt.Mix well.
Add the ricotta and lemon zest.
Mix until nicely incorporated and no lumps are left.
Pour into the pan and bake for about 25-30 minutes or until you see the edges turning golden and a toothpick inserted in the center comes out clean.Let it cool for a bit before transferring it onto a wire rack to cool completely.
Dust with powdered sugar and serve!