Preheat oven to 350F and grease a 10-12 cup Bundt pan with cooking spray.
In a medium bowl, whisk flour, baking powder, baking soda, salt, and poppy seeds until well combined.
Using a stand mixer fitted with the paddle attachment, beat butter until smooth.
Add sugar and beat on med-high until pale and fluffy (2-3mins).
Reduce speed and add eggs one at a time, fully incorporating after each addition.
Add vanilla, sour cream, lemon zest, and lemon juice. Beat well to combine.
Alternate adding flour mixture and milk, beginning and ending with flour (3 additions of flour and 2 of milk). Fully incorporating after each addition. Do not overmix.
Add some batter into your prepared pan and press it into the cracks of the bundt pan with a small spatula. Add remaining batter until pan is no more than 3/4 full. Smooth the top with a spatula and whack the pan against the counter to evenly distribute.
Bake for 50mins or until a toothpick inserted into the center comes out mostly clean.
Place cake on wire rack to cool for 10mins. Whack the pan on the counter to loosen the cake and turn out onto wire rack.
Cool completely before dusting with powdered sugar.