Preheat the oven to 350 F.
Butter and flour (or use baking spray) a 12 cup bundt pan. Make sure you get into all the crevices so the cake will be easy to remove from the pan.
In the bowl of a stand mixer, rub together the zest and sugar with your fingers. Once the sugar is wet and the oils have been released add the butter, vanilla and salt. Beat until very light and fluffy, scraping down the bowl as needed. This will take 5-7 minutes.
Add the eggs, one at a time, with the mixer on low. Scraping down as needed to ensure all the batter is evenly mixed.
Sift in the cake flour with the baking powder and soda and use a rubber spatula to fold the flour into the batter (this way when you turn the mixer on the flour won’t fly out). Turn the mixer on low and pour in the buttermilk, slowly. Once it’s well blended add the poppy seeds and mix. Pour the batter into the bundt pan and bake until a cake tester comes out clean - about 50 minutes. Let cool in the pan for 10 minutes, then invert it onto a plate.
When the cake is cool, whisk together the glaze ingredients and pour over the cake. Top with poppyseeds.