Preheat the oven to 325°F. Line the bottom of a 9" or 10" springform pan with parchment., To make the cake: In a large mixing bowl, combine the egg yolks, 2 tablespoons of granulated sugar, and salt. Whip until the yolks are light and lemon-colored, then gradually drizzle in the oil with the mixer running at high speed. Mix in the lemon juice and zest. Scrape the sides and bottom of the bowl., Sift the flour and cornstarch together, then fold into the egg yolk mixture., In a separate bowl with a clean whisk, beat the egg whites until foamy and white. With the mixer running at medium-high speed, gradually add the remaining granulated sugar. Increase the mixer's speed to high and whip until a smooth, glossy meringue forms. It should hold a medium peak (the tip will slowly flop over when you pull the whisk up out of the mixture)., Fold the meringue into the egg yolk/flour mixture, mixing until no streaks of egg white remain., Scoop the batter into the prepared pan, and use an offset spatula to lightly smooth the top. Bake for 50 to 65 minutes, until the top is golden brown and the center springs back when lightly touched. If using a 10" pan, and/or its surface is dark instead of light, check the cake at 40 minutes. Add more time in 5 minute increments as needed for the center to be set., Remove the cake from the oven and cool it completely in the pan., To make the topping: Whip the heavy cream with the zest, lemon juice, and sugar until light and pillowy, and it just barely holds a peak., To serve: Run a thin spatula around the outside edge of the pan before releasing the hinge. Pull off the outer ring and use a large spatula under the parchment to transfer the cake to a serving plate. Dust the top of the cake with confectioners' sugar; slice, and serve with a dollop of the topping., Store any leftovers at room temperature, well wrapped, for several days; freeze for longer storage. Keep any leftover topping refrigerated.