Whisk together 140 grams masa harina, 100 grams granulated sugar, 28 grams cornstarch, 2 teaspoons baking powder, and 1/2 teaspoon table salt together in a medium bowl. Set aside.
Stir together 170 grams milk and 1 teaspoon vanilla extract in a measuring cup. Set aside.
Separate 3 large eggs, being sure not to get any yolks into the egg whites (it's best to separate the eggs one at a time, to reduce the amount of waste in case any of the yolks break).
Add the egg whites to the bowl of a stand mixer and mix on medium speed until the egg whites hold a medium peak. Add one of the egg yolks and beat on medium speed until the yolk is fully incorporated. Repeat with the second, and then the third egg yolk, waiting for each to be incorporated before adding the next.
Sprinkle half of the masa harina mixture over the egg white mixture and fold gently with a spatula, trying to avoid deflating the egg whites, until the dry ingredients are completely incorporated.
Add half of the milk mixture and fold until the milk is completely incorporated. Fold in the remaining dry ingredients, and then the remaining milk. Allow the batter to rest in the mixing bowl for 15 minutes.
While you're waiting for for the batter to rest, Move oven rack to middle position. Heat oven to 350°F. Grease a 8x8" baking pan with canola oil or butter and dust lightly with masa harina. Tap out any excess.
Pour the batter into the prepared baking pan and spread evenly into the pan with a spatula. Bake until the top is golden brown, and a toothpick inserted into the center of the cake comes out with just crumbs clinging to it, 35-40 minutes.
While the cake is baking, stir together 354 milliliter evaporated milk and 300 milliliter sweetened condensed milk in a large measuring cup or small bowl with a pouring spout.
While the cake is still hot, poke holes all over the cake with a chopstick or skewer (make sure the hole goes all the way to the bottom of the cake, but avoid using something sharp to make the holes so you don't scratch your pan).
Pour the soak over the cake very slowly, letting it soak in. If you get to a point where the cake will no longer absorb more soak, and there's a layer sitting on top of the cake after several minutes, stop adding more. Cover the cake with plastic wrap and cool completely in the fridge, at least 2 hours. Remove the cake from the fridge 30 minutes before sitting to warm up a bit.
Just before serving, add 3/4 cup whipping cream and 1 Tablespoon granulated sugar to a medium bowl. Whip the cream at high speed until it reaches medium-stiff peaks (you don't want it to be so soft that it runs off your cake slices, but you don't want to overwhip it and turn it to butter either).
Spread the whipped cream over the cake, then cut into squares and serve. Cover the pan with plastic or transfer any leftovers to an airtight container to store in the fridge for up to 2 days (note that this cake is best when eaten fresh).
Notes
You can also use a 9x9' baking pan, but the cake will not be as tall.Cans of evaporated milk and sweetened condensed milk seem to vary slightly in size between the US and Canada, by a couple of ounces, and the units may vary (in Canada, both are sold by volume whereas in the US, sweetened condensed milk is sold by weight and evaporated milk by volume). These small variations should not affect the recipe significantly, and it's okay to just use the whole cans, as long as they're somewhat close.