
Preheat the oven to 350°. Beat the butter and sugar in the bowl of an electric mixer fitted with a paddle attachment on medium until light and fluffy, about 5 minutes. With the mixer on medium speed, add the eggs, one at a time, beating well after each addition, stopping to scrape the sides of the bowl as needed. Stir in the vanilla extract and lemon zest.
Stir together the flour, salt, baking powder, and baking soda in a medium bowl. Stir together the buttermilk, poppy seeds, and lemon juice in a small bowl.
Gradually add about one third of the flour mixture with the mixer on medium-low. Stir in half of the buttermilk mixture followed by another third of the flour mixture. Repeat with the remaining buttermilk and flour mixtures until all is incorporated.
Spray a 12-cup Bundt pan with nonstick baking spray. Pour the batter in the prepared pan. Bake until a wooden pick inserted in the center comes out clean, 45 to 55 minutes. Cool cake in the pan for 10 minutes.
Turn the cake onto a wire rack and cool completely, about 2 hours.
For the glaze: Whisk together the powdered sugar and lemon juice in a small bowl. Drizzle the glaze over the cake, allowing it to drip down the sides. Let the glaze harden for at least 15 minutes before slicing and serving.