Preheat the oven to 325℉. Spray a 12-cup fluted tube cake pan with baking spray (or rub with shortening and dust with flour).
In a medium bowl, whisk together the flour, baking soda and salt. In a large bowl, use an electric mixer to combine the sugar and butter until light and fluffy (2 minutes). Beat in the eggs, one at a time.
On low speed, mix in the flour alternately with the buttermilk, scraping the bowl occasionally until the flour is mixed in. Stir in the poppy seeds, lemon zest and lemon juice. Scrape the batter into the prepared pan.
Bake 50 to 55 minutes, or until a toothpick inserted into the center comes out clean.
PREPARE GLAZE & FINISH THE CAKE:
While the cake is baking, prepare the glaze. In a medium bowl, whisk together the glaze ingredients until smooth; cover and set aside.
When the cake comes out of the oven, poke several holes in the the cake with a skewer (while it is still in the pan). Stir the glaze. Pour about ¼ of the glaze on top of the cake. Set the glaze aside. Cool the cake in the pan for 20 minutes.
Invert the cake onto a serving plate. Let the cake cool for about an hour. Then drizzle the glaze on top of the cake (heat it a little in the microwave, if needed), allowing some to drizzle down the sides.