Position a rack in the center of the oven and preheat to 325ºF (160ºC). Butter and flour a 10-inch tube or Bundt pan very thoroughly.
Scrub the lemons with warm soapy water to remove any excess wax, then dry the fruit. Put the sugar into a medium bowl and zest the lemon directly into the sugar. Use your fingers to rub the zest into the sugar until evenly distributed and fragrant.
Sift the flour, baking soda, salt, and poppy seeds together in a bowl. In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl with an electric mixer, mix the butter and cream cheese on medium speed for about 2 minutes. Add the sugar and zest mixture and turn the mixer up to medium high. Mix for 3-5 minutes, making sure to scrape down the bottom and sides of the bowl with a rubber spatula periodically. The butter and sugar should be light, fluffy, and fragrant.
Add the eggs one at a time, mixing for about 30 seconds after each addition. Periodically stop the mixer and scrape the bottom and sides of the bowl to ensure even mixing. Add the vanilla and mix until combined.
On low speed, add the milk, followed by half the flour mixture, and mix until just combined. Add the lemon juice, and then the remaining flour mixture, and mix until just combined. Remove the bowl from the mixer and give the mixture a few more turns with a spatula to make sure it’s combined completely. Pour half the batter into the prepared pan. Take 1/2 cup lemon curd and drop it in circles over the cake batter. Using an offset spatula or butter knife, drag the lemon curd through the top of the batter, making swirls. Top with the remaining half of the cake batter, and repeat the swirls with the remaining 1/2 cup of the lemon curd. Tap the pan lightly on the counter to remove any large air bubbles.
Bake the cake until it is golden and a cake tester inserted in the center comes out clean, 60 to 75 minutes, depending on the pan. Let the cake cool in the pan for 20 minutes, then carefully unmold it onto a rack to cool a bit more before glazing.