Preheat your oven to 325 degrees F. Prep your pan by lightly spraying all the sides and crevices of a 12 cup pan. Set aside.
In a medium sized mixing bowl, whisk together the cake flour, baking powder, lemon zest, and salt. Set aside.
In the bowl of an electric mixer fitted with the paddle attachment, cream the butter, oil, and the sugar for 3 minutes on medium-high speed. The color will start getting lighter.
With a rubber spatula, scrape down the sides of the bowl and begin to add the egg whites and whole eggs on medium speed, scraping down the sides and bottom of the bowl between additions. Once all the eggs have been added, beat the mixture on medium-high speed for an additional 2 to 3 minutes.
Add the sour cream and the lemon flavoring of your choice and mix on low. If it starts to look a little curdled, don’t stress, once you add the flour, it will smooth out.
Turn the mixer to the lowest speed, add ⅓ of the flour mixture, followed by half of the buttermilk, repeat, ending with the flour. Remember to be on the lowest speed to prevent over mixing. Scrape the bottom of the bowl, and mix on low for 20 more seconds.
Pour the cake batter into the prepared bundt pan and bake for 40-45 minutes or until a toothpick inserted in the center of the cake comes out with only a few moist crumbs on it.
Allow the cake to cool in the bundt pan completely before transferring it out of the bundt pan and onto a plate for serving.
(Optional: To help bring out the lemon flavor more, create a lemon simple syrup by combining ¼ cup water, ¼ sugar, ¼ teaspoon lemon extract in a bowl and microwave until the sugar dissolves, brush on top of the bundt cake with a pastry brush.)
Make the glaze by combining all ingredients in a small bowl and using a whisk or a fork to getting any lumps out. Pour the glaze over the top of a cooled cake and serve.