Adjust oven rack to lower-middle position and heat to 350 degrees. Coat the inside of a 12 cup Bundt pan thoroughly with the baking spray.
Whisk the flour, 1 1/2 cups of sugar, zest, salt, baking powder, and baking soda together in a bowl. In a separate bowl whisk the milk, egg yolks, oil, melter butter and Elderflower Cordial together.
In a large bowl whip the egg whites and cream of tartar with an electric mixer on medium-low speed until foamy, about 1 minute. Add the remaining 1/2 cup sugar and continue to whip on medium-high until peaks are stiff and glossy.
Whisk the milk mixture and lemon juice into the flour mixture until smooth. Fold in the egg whites with a rubber spatula until combined.
Scrape the batter into the prepared pan, wipe off any drips and gently tap the pan on the counter to settle the batter.
Bake cake until a toothpick comes out with a few moist crumbs attached, 40-45 minutes, rotating the pan halfway through the baking.
Let the cake cool in the pan for 10 minutes then flip it out onto a wire rack. If needed, gently separate from sides of pan with a skinny rubber spatula. Let cool completely, about 2 hours.
In a small bowl whisk together the glaze ingredients, zest optional. Drizzle the glaze evenly over the top of the cake letting it drip down the sides. Let sit 15 minutes before serving. Enjoy!