Preheat the oven to 325 degrees. Coat a 12-15 cup bundt pan with cooking spray with flour, such as Baker’s Joy. Zest your lemons before juicing them. Set aside.
In a large measuring cup, whisk together the milk, lemon juice, eggs, and vanilla extract.
In the bowl of an electric mixer, whisk together the flour, cornstarch, granulated sugar, lemon zest, baking powder, baking soda and salt until well combined.
With the beater attachment in place and the mixer on low speed, begin adding the butter in small Tablespoon sized pieces. Continue to beat until all the butter is added, and the mixture is in small crumbs.
Pour in ¾ of the milk mixture. Increase the speed to medium and beat until the batter is pale and fluffy, 1-2 minutes, scraping down the bowl as needed. Add the remaining milk and beat for a final time, on low to start and then on high for another minute, scraping down the bowl halfway.
Pour the batter evenly into the prepared pan and smooth the top. Bake on the center rack until the top is golden and a toothpick inserted in the center comes out with just a few moist crumbs, 60-70 minutes. Let cool for at least 15 minutes before placing a wire rack on the top of the bundt pan and inverting it.
Meanwhile, prepare the glaze. In a saucepan, combine the sugar, butter, and lemon juice. Set the pan over medium heat and cook, stirring until the sugar is dissolved. While the cake is still warm, use a pastry brush to soak the cake with the glaze. You’ll likely need to make several passes over the cake before it is all soaked in. Let the cake cool completely.
Combine the powdered sugar, cream, vanilla, and salt in a bowl and whisk until smooth. Pour the icing over the cake, letting it cascade over the sides. Let it set before slicing and serving.