Preheat oven to 350 degrees F. Position the oven rack on the lower third position.
Spray a bundt pan with non-stick cooking spray or generously grease with butter. Set pan aside.
Add flour (or flour/cornstarch mixture) into a large bowl. Whisk in the salt, baking powder, baking soda and the poppy seeds. Set bowl aside.
Using an electric mixer, beat the butter on high speed until it’s smooth and creamy (approx. 1 minute).
Add the granulated sugar and beat on high speed for 2 more minutes until creamed together thoroughly. Make sure to scrape down the sides a couple of times with a rubber spatula.
Add the eggs and vanilla to the creamed butter and sugar and beat on medium-high speed until they are combined. Scrape down sides and bottom of bowl as needed.
Beat in the lemon zest and lemon juice.
With the mixer on low, start adding the dry ingredients and buttermilk. Do this in 3 additions, starting and finishing with the flour and only mixing each addition just until incorporated. Do not over mix! This will create a thick batter.
Pour the batter into the prepared bundt pan. Use a spoon or spatula to help distribute the batter evenly because the thick batter will not even out on it’s own.
Bake for 40 to 50 minutes. Check at the 40 minute mark by inserting a toothpick to see if it comes out clean. Once the cake is done, remove from oven and allow to cool in the pan for 10 minutes. During this time, prepare the lemon syrup. (See lemon syrup recipe below.)
Remove the bundt cake from the pan and place it on a cooling rack with parchment paper under and then using a pastry brush, brush the Lemon Syrup all over the bundt cake; allow the cake to cool.
Prepare the Lemon Glaze (see recipe below) and using a pastry brush, brush the glaze to cover the entire bundt cake. Allow the cake to cool for at least ten minutes before cutting and serving.