Preheat the oven to 350 degrees F. Grease an 8-inch or 9-inch round cake pan and line it with parchment paper (note: the 8-inch pan cuts it a bit close with the batter when the cake rises in the oven but won't spill over). Place the cake pan on a baking sheet.
In a medium bowl, whisk together the flour, cornstarch, baking powder, kosher salt and lemon zest (make sure the zest doesn't clump together). Set aside.
In a stand mixer fitted with the paddle attachment, cream the butter and sugar together for several minutes until light and fluffy (first on low speed and then gradually increasing the speed to medium high). Turn off the mixer and scrape down the sides of the bowl with a spatula.
Turn the mixer back on low speed and slowly add the eggs, one at a time, scraping down the bowl after the second egg. Allow the eggs to incorporate completely and then scrape down the bowl again. (This is a lot of eggs so don't worry if the mixture starts to break. The flour mixture will bring it back together.)
Add the crushed pineapple along with the vanilla and mix very briefly on medium low to combine. (The texture of the crushed pineapple and juice WILL make the batter look broken.) With the mixer on low, add the flour mixture in 3 batches and mix until just combined. Turn off the mixer and scrape down the bowl with a spatula, giving the batter one final stir.
Pour the batter into the prepared cake pan and use a spatula to level off the top.
Bake for 50-60 minutes, or until a toothpick comes out clean. Allow to cool for at least 15 minutes before removing the cake from the pan. Serve plain or with freshly whipped cream.
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Notes
You want pineapple canned in juice, not in syrup.
Don't drain the canned pineapple. You want all of the pineapple juice in the cake for both flavor and moisture! This cake will not work if you substitute fresh pineapple.