Preheat the oven to 325°. Butter and flour a 2-quart loaf pan (10 by 5 by 3 inches). In a bowl, sift together the flour, polenta and salt.
In a standing electric mixer fitted with the paddle, beat the sugar and butter at medium speed until light and fluffy. Add the eggs, 1 at a time, beating just until each is incorporated. Add the orange-flower water and orange zest and beat until blended. Mix in the dry ingredients at low speed until thoroughly moistened, scraping the side and bottom of the bowl as necessary.
Spread the batter in the prepared pan and smooth the surface. Bake in the center of the oven for about 2 hours, or until a toothpick inserted in the center of the cake comes out clean. Let cool in the pan for 10 minutes, then turn it out onto a wire rack to cool completely.