Sift flour, baking powder and salt into a mixing bowl.
In a large stand mixer bowl, cream together the butter, ricotta, and sugar, then adding eggs, one at a time, allowing each to incorporate before adding the next. Add vanilla.
Set mixer speed to low, and gradually add the dry ingredients. Once added, allow the batter to mix for 30 seconds or so.
Pour the batter into the prepared loaf pan, smoothing the batter.
Bake the cake on the center rack for 15 minutes, then lower heat to 325°F (160°C) and bake about 25-60 minutes more, or until cake springs back from touch and has slightly pulled away from pan sides, and a toothpick comes out clean (baking time is approximate: the amount of water in the ricotta determines the baking time in the end).
Cool the cake inside the loaf pan for 15 minutes before removing. Allow the cake to finish cooling outside the pan from then on.