01 - Preheat the oven to 350°F. Generously grease and flour a 10–12 cup bundt pan, ensuring all crevices are coated to prevent sticking.
02 - In a medium bowl, whisk together the flour, poppy seeds, baking powder, baking soda, and salt until evenly distributed. Set aside.
03 - In a large bowl, beat the softened butter and granulated sugar together on medium-high speed until the mixture is pale and fluffy, approximately 3–4 minutes.
04 - Add the eggs one at a time, beating well after each addition to ensure full emulsification. Mix in the lemon zest, lemon juice, and vanilla extract until combined.
05 - With the mixer on low speed, alternately add the dry flour mixture and the combined sour cream and milk, beginning and ending with the flour mixture. Mix until just combined to avoid overworking the gluten.
06 - Pour the batter evenly into the prepared bundt pan and smooth the top with a spatula to ensure even baking.
07 - Bake for 45–50 minutes, or until a wooden toothpick inserted into the center of the cake comes out clean.
08 - Allow the cake to cool in the pan for 15 minutes before carefully inverting it onto a wire rack to cool completely.
09 - In a small bowl, whisk together the powdered sugar, lemon juice, heavy cream, and lemon zest until smooth and pourable. Adjust consistency with additional cream or sugar if necessary.
10 - Once the cake has cooled completely, drizzle the glaze over the top of the cake. Allow the glaze to set slightly before slicing and serving.