Preheat the oven to 350 degrees F. Grease a 9-by-5-by-3-inch loaf pan with butter. In a medium bowl, combine the flour, baking powder and salt. Stir to blend.

Using a mixer, cream the butter, ricotta and granulated sugar until light and fluffy, about 3 minutes. With the machine running, add the eggs 1 at a time. Add the vanilla, orange zest and amaretto until combined. Add the dry ingredients, a small amount at a time, until just incorporated.

Pour the batter into the prepared pan and bake until a toothpick comes out clean and the cake pulls away from the sides of the pan, 45 to 50 minutes. Let cool in the pan for 10 minutes, then transfer to a rack to cool completely. To wrap, return to the pan and dust with confectioners' sugar.