In a medium bowl, combine the sour cream and poppy seeds. Cover and let sit for 2 hours or up to overnight in the refrigerator. 

Preheat the oven to 350°F. Grease and flour a 10-12” bundt or tube pan and dust with flour.

Place the eggs in a large bowl and whisk to combine. Add the sugar and mix to combine. Add the poppy seed mixture and mix to combine. Add the butter and mix to combine. Add the flour and salt and mix to combine. Fold in the lemon zest.

Sprinkle the baking soda over the top of batter. Pour the vinegar directly over the baking soda. It will foam! Immediately start whisking vigorously until combined (an old Russian baking trick!).

Pour the batter into the prepared pan and bake until the cake pulls away from the sides of the pan, the top is a deep golden brown, and a tooth pick inserted near the center comes out clean, about 45-50 minutes. 

Let cool then turn out of the pan and dust with confectioner’s sugar before serving.