Preheat your oven to 350 degrees, and grease and line a quarter-sheet pan with parchment paper. This is a bit of an odd mixing method, but go with me here: In a large bowl, add all the ingredients (softened butter, sugar, sour cream, lemon zest, lemon juice, eggs, flour, baking powder, and salt). Use an electric mixer to mix the ingredients together until just combined. Your batter should be thick, and you may have a couple of small chunks of butter running through, which is totally fine!

Spread the batter evenly in your prepared cake pan and bake for 10-15 minutes, or until the cake is set and a toothpick inserted into the center of the cake comes out with just a few crumbs. Cool the cake completely before adding the topping.

In a small bowl, mash the raspberries with a fork until they are roughly mashed, but there are still a few chunks of raspberries. Stir in the raspberry jam and set this mixture aside. In a medium bowl, whip the heavy cream until you have stiff peaks. Gently fold in the lemon curd, reserving 1-2 tbs, until well combined. Spread the raspberry mixture over the top of the cooled cake. Then, evenly spread the lemon cream mixture on top. Dollop the remaining lemon curd over the top, and use the back of a spoon to swirl the mixture together. Wrap the cake and chill for at least an hour, and then slice and serve!