Preheat your oven to 350 degrees and spray an 8x8 inch cake pan with baking spray. Line the pan with parchment paper that has overhanging edges for easy removal.

In a large bowl, add your butter, oil, sugar, lemon zest, eggs, sour cream, lemon extract, flour, baking powder, and salt. Mix everything together at once until a thick batter forms- this is an odd mixing method but it works! You want everything to just come together, but the batter will be thick.

Spread the batter evenly into your prepared baking pan. Dollop the lemon curd all over the top of the cake, and use a knife to gently swirl the lemon curd into the cake. Bake for 20-25 minutes, or until a toothpick inserted into the center of the cake comes out with just a few crumbs clinging to it. Cool the cake completely in the pan before adding the topping and serving.

In a medium bowl, whip the heavy cream until stiff peaks have formed. Beat in the lemon curd and salt until well combined and smooth. Top the cake generously with your whipped cream mixture, optionally swirl in some extra lemon curd, and enjoy!