Preheat the oven to 350 F. Butter and flour the bundt pan. Or may use 2 9 x 5 inch loaf pans, line with parchment paper. Soak the poppyseeds in the milk and 1/4 cup lemon juice and set aside. With the remaining 1 cup of lemon juice and 1/2 cup sugar, bring to a boil and reduce to 1/2 cup of liquid and set aside.

Using a stand mixer cream the butter and 2 cups of sugar together until light and fluffy. Add the eggs one at a time, mixing on medium speed. Add the vanilla and lemon zest.

In a separate bowl, mix the flours, cornstarch, salt, baking soda and powder. Add the sour cream to the poppyseed mixture. Alternate adding the flour mixture and poppyseed mixture to the butter mixture, starting first with the flour and ending with flour at the end.

Pour the batter into the prepared pan(s). Bake for 40-50 minutes for bundt, 50-60 minutes for the loaf pans until a toothpick inserted in the center comes out clean.