Preheat your oven to 350°F. Oil a 9 x 5-inch non-stick loaf pan and dust with flour.

Whisk together the flour blend, baking powder, baking soda, and salt; set aside.

Using an electric mixer fitted with its paddle attachment, beat the butter on medium speed until smooth, scraping bowl at least once midway through mixing.

Mix in the sugar, ½ cup at a time, on medium speed until fluffy, 3 - 4 minutes.

Add the eggs, one at a time, beating after each addition until combined. Scrape the sides and bottom of the bowl, as needed.

Add the sour cream and vanilla, and if using, lemon zest. Beat on low speed just long enough to combine.

Sift one-third of the flour mixture at a time into the batter, beating after each addition and scraping bowl.

Transfer the batter to the prepared loaf pan, and distribute evenly.

Bake on center rack of the preheated oven until the center no longer jiggles, about 55 - 60 minutes. Test for doneness every 5 minutes beginning at 55 minutes. To test, insert a skewer near the center. When you remove it and it comes out clean, it's done. (Note: The cake being a tiny bit underdone is better than overdone because it will continue to bake slightly when cooling in the pan.)

Transfer the pan to a wire rack to cool in the pan for 15 minutes. Remove the cake from the pan and transfer it directly to the wire rack to cool completely, 1-½ to 2 hours.

Serve the pound cake within 24 hours or slice, wrap in individual servings in plastic wrap and freeze in a gallon-sized storage bag. Defrost frozen slices at room temperature.

Whisk together the confectioners' sugar and lemon juice (or milk, if not making a lemon pound cake) until smooth.

Drizzle icing over the top of the cake and allow it to drip down the sides.