Directions

1. Heat oven to 350 degrees. Place two racks in center of oven. Butter three 8-by-2-inch round cake pans; line each with a circle of parchment paper. Butter paper, and dust pans with flour; tap out excess. Set aside.
2. Sift together flour, baking powder, and salt in a medium mixing bowl. Set aside.
3. In the bowl of an electric mixer fitted with the paddle attachment, cream butter on medium-low speed until lightened, 1 to 2 minutes. Gradually add sugar; beat until color has lightened, 3 to 4 minutes, scraping down sides of bowl once or twice. Drizzle in eggs, a little at a time, beating on medium-low speed after each addition until batter is no longer slick but is smooth and fluffy, about 5 minutes. Stop to scrape down bowl once or twice so batter will combine well. Beat in vanilla on medium-low speed.
4. Reduce the mixer speed to low. Alternately add reserved flour mixture and milk, a little of each at a time, beginning and ending with flour mixture. Scrape down the bowl once or twice. Beat in lemon zest, orange zest, lime zest, and 1/3 cup poppy seeds.
5. Divide batter evenly among the prepared pans. Bake 30 minutes, then rotate pans for even browning. Bake until a cake tester inserted into center of cakes comes out clean, 5 to 10 minutes more. Transfer to wire racks to cool, 15 minutes. Turn out cakes, and set on racks, tops up. Cool completely.
6. Remove parchment from bottom of each layer. Save best-looking layer for the top. Place one layer on the serving platter. Spread 1 1/2 cups cream-cheese frosting over the top. Place second cake layer on top, and spread remaining 1 1/2 cups frosting over top. Place reserved layer on top. Chill cake, loosely covered with plastic wrap, 1 hour.
7. To serve, stir lemon glaze well, then pour onto center of top layer of cake, letting it run down the sides. Using a single-hole zester, cut long strips of zest from orange and lemon, if desired. Arrange zest in loose spirals on the top of cake, and sprinkle lightly with poppy seeds.