In a small bowl, sift together the cake flour, baking powder and salt.
In a large bowl, using an electric mixer, beat the ricotta, butter and sugar until smooth. Beat in the eggs one at a time. Beat in the vanilla. Stir in the orange zest with a spatula.
Stir in the dry ingredients in 3 batches just until incorporated (you can use a beater for this step but I find the orange zest gets stuck in my beaters and I want it to stay in the cake).
Pour the batter into the cake pan and bake for about 50 minutes or until a toothpick comes out with a few crumbs.
Cool on a rack for 15-20 minutes. Remove from pan and leave on rack until completely cooled. Serve on a pretty cake platter and dust with Powdered Sugar.
Notes
You can also make this in a loaf pan if you want a more traditional "pound cake" shape.