Heat the oven to 350°F with a rack in the middle position. Mist a 9-inch round cake pan with cooking spray. Using a chef's knife, cut the kernels from the ears of corn.
Measure 250 grams (1½ cups) kernels and add to a blender; if you have extra corn, reserve it for another use. To the blender, add the cornmeal, condensed milk and yogurt, then puree until smooth, 15 to 20 seconds, scraping down the blender as needed.
Let stand for 10 minutes. Meanwhile, in a small bowl, whisk together the flour, cornstarch, baking powder and salt.
To the blender, add the whole eggs and yolks, and the oil; blend on low until smooth, 5 to 10 seconds. Pour the puree into a large bowl.
Add the flour mixture and whisk just until evenly moistened and no lumps of flour remain. Transfer to the prepared cake pan and bake until golden and a toothpick inserted into the center of the cake comes out clean, 40 to 45 minutes.
Cool in the pan on a wire rack for 30 minutes. Run a paring knife around the pan to loosen the cake, then invert directly onto the rack and lift off the pan.
Re-invert the cake onto a serving platter and cool completely, about 1 hour. Serve dusted with powdered sugar.