Prepare a double boiler by filling the bottom pot with 1 to 2 inches of water (the water should not be touching the bottom of the top bowl). Bring water to a boil and reduce heat to medium-low.
Place granulated sugar, whole egg, egg yolks, and lemon zest in the top pot of the double boiler. Start whisking immediately until well combined.
Slowly add the lemon juice while continuing to whisk and cook the curd.
Once the mixture becomes slightly wobbly and thickened (about 10 minutes), remove pan from heat.
Add the sliced butter and salt into the curd. Whisk until the butter has completely melted and the curd is well combined.
Pour curd into a bowl and immediately place a piece of plastic wrap on top (it should be touching the surface of the curd or a skin layer will form).
Place the lemon curd in the refrigerator and allow it to cool and continue to thicken. NOTE: This recipe makes more lemon curd than required, you will have leftovers.
Single Layer Lemon Cake
Preheat oven 350 °F to and center oven rack.
Prepare an 8 inch cake pan by placing a parchment circle in the bottom of your cake pan. Liberally spray it with non-stick cooking spray.
In a medium sized bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt. Set aside.
In a small measuring cup combine buttermilk and sour cream. Set aside.
Using a hand mixer or stand mixer, cream together the room temperature unsalted butter, granulated sugar, and lemon zest until pale in color and fluffy (about 3-4 minutes at medium- high speed). Scrape down bowl with a spatula as needed.
Add eggs one at a time and beat on medium speed until incorporated.
Add vegetable oil and vanilla extract, beat on medium speed until incorporated.
On low speed, alternate adding the dry ingredients and buttermilk mixture. Between each addition scrape down the bowl. It should go like this: dry ingredients, buttermilk mixture, dry ingredients, buttermilk mixture, dry ingredients, STOP and move onto next step.
Pour lemon cake batter into the prepared cake pan and smooth it into an even layer.
Bake for 35 to 45 minutes, or until a toothpick inserted into the center of the cake comes out clean.
Remove from oven and immediately run a knife around the perimeter of the cake to detach it from the pan. Allow the cake to cool for 10 to 20 minutes inside the pan.
Carefully invert the cake onto a wire rack and allow it to completely cool.
Cream Cheese Whipped Cream
On medium-high speed beat the cream cheese and vanilla extract. It should be light in color and smooth.
Add the powdered sugar and cream together on medium-high speed until smooth.
Turn the mixture to medium speed and slowly pour in the heavy whipping cream. Once added, turn speed to high and allow the frosting to come to stiff peaks (about 30 seconds to 1 minute, the frosting will be able to hold it's shape).
Decorating the Lemon Curd Cake
Place the completely cooled cake on a cake plate or serving plate.
Spread the cream cheese whipped cream frosting over the top of the cake until it is in an even layer.
Scatter spoonfuls of the lemon curd over top of the frosting. Lightly swirl it using your icing spatula to give a marbled effect.
Cut into 10 equal pieces and serve.
Video
Notes
Storing Information:
Leftover Lemon Curd: Store in a glass jar, in the refrigerator, for up to 10 days. Freeze in an airtight container for up to 6 months.
Lemon Curd Cake: Refrigerated, in an airtight container, for up to 3 days. This cake can be kept at room temperature for a day or so (out of direct sunlight. I do not recommend this cake be frozen.
Make Ahead Information:
The lemon cake should be cooled, wrapped in plastic wrap, and stored in the refrigerator. The lemon curd can be kept in an airtight glass container or jar. Both can be made up to 2 days in advance.
Do not prepare the cream cheese whipped cream until you are ready to decorate and serve the cake.
Use Different Sized Pans:
This recipe will make other single layer cakes like a bundt cake or 8×8 square cake. You can even double the recipe to make a 13×9 cake.