• Prepare for baking. Preheat the oven to 350ºF. Lightly grease a 9-inch springform pan with cooking spray and set aside.

Make the Simple Syrup

• Combine the ingredients. Combine the water, sugar, lemon juice, and orange peels in a saucepan set over high heat; bring the mixture to a boil.
• Simmer. Reduce to a simmer and let simmer for 5 minutes.
• Cool. Remove from heat and let cool completely. Refrigerate until ready to use.

Make the Cake

• Mix the dry ingredients. In a mixing bowl, combine the flour, semolina, and baking powder, whisking until well incorporated, and set aside.
• Cream the butter and sugar. Using a stand mixer, cream together the butter and sugar until light and fluffy, about 3 to 4 minutes.
• Add the eggs. Then, start adding the egg yolks, one at a time; mix until blended and the batter is a light yellow. Add the vanilla extract and lemon zest.
• Add the dry ingredients. On LOW speed, add in the flour mixture, about ½ cup at a time until blended.
• Add milk. Then slowly add in the milk; continue to mix until well incorporated. Set aside.
• Whip the egg whites. Using a separate bowl, beat the egg whites with a pinch of salt until soft white peaks form.
• Combine. Using a spatula, carefully fold the egg whites into the cake batter; do not overmix.
• Fill the pan. Scrape the cake batter into the previously prepared springform pan and spread it evenly.
• Bake. Bake for 35 to 40 minutes, or until a toothpick inserted in the center comes out clean. Remove the cake from the oven and transfer it to a wire rack; let it cool for about 10 minutes.
• Add the simple syrup. Using a sharp knife, cut the cake into a diamond pattern, but don't separate the slices just yet. Slowly pour the cooled syrup all over the hot cake. Let the cake cool completely.
• Garnish and serve. Top with powdered sugar (optional). Remove the cake from the pan, and serve.