Lower the oven rack to the lower third position and preheat oven to 350°F (177°C). Spray a 10-inch bundt pan with cooking spray and set aside.
In a large bowl, sift together the flour and cornstarch. Whisk in the salt, baking powder, baking soda and poppy seeds. Set aside.
In a large mixing bowl, beat the butter and sugar together on high speed until pale and creamy (about 2 minutes). Scrape down the sides of the bowl with a spatula as needed. Mix in the eggs one at a time, and add the vanilla. On low speed, mix in the lemon juice, lemon zest and oil.
With the mixer on low speed, add the dry ingredients in 3 additions, alternating with the yogurt, beginning and ending with the dry ingredients. Mix each addition until just incorporated. Do not overmix.
Spoon the batter into the prepared pan and evenly distribute it. Bake for 45-55 minutes or until a toothpick inserted into the cake comes out clean. My cake was done at 50 minutes. Check on the cake in the last 15 minutes of cooking: if the top seems to be browning too much, cover the cake with aluminium foil until it's finished baking. Once done, remove from oven and allow to cool inside the pan for 10 minutes.