Step 1

Whisk together the sugar, egg yolks, and cornstarch in a medium saucepan.

Step 2

Once smooth and well combined, whisk in the lemon zest and juice.

Step 3

Cook over medium heat until thickened, occasionally stirring (using a rubber spatula) at the beginning but constantly mixing near the end. It should take about 8-10 minutes on a gas stove top or 20 minutes on an electric stove top.

Step 4

Remove from heat and toss in the butter. Stir until melted and combined.

Step 5

Pour the curd into a wide and shallow heat proof container. Cover the container and let it chill while we bake the cake.

Step 6

Preheat the oven to 350F and grease and line a 9×13 baking dish with parchment paper.

Step 7

In a medium bowl, whisk together the flour, cake flour, baking powder, baking soda, salt, and poppy seeds.

Step 8

In a measuring glass, mix together the milk and sour cream.

Step 9

In a large mixing bowl, add the sugar and lemon zest. Rub the zest into the sugar using your fingers. This will help release even more lemon flavor.

Step 10

Now whisk in the oil and melted butter, followed by the eggs, lemon juice, and vanilla.

Step 11

Pour in half of the dry ingredients and whisk.

Step 12

Right before it’s combined, pour in the milk and sour cream and whisk.

Step 13

Add in the rest of the dry ingredients and whisk until everything is smooth and combined.

Step 14

Pour the batter into the prepared baking dish and bake for 30-35 minutes or until a toothpick in the center comes out clean with a few moist crumbs.

Step 15

Allow the cake to cool completely before frosting.

Step 16

In a mixing bowl using a hand or stand mixer with the paddle attachment, mix together the cream cheese and butter until smooth.

Step 17

Then mix in the powdered sugar one cup at a time, followed by the vanilla.

Step 18

Once the cake has cooled, lift it out of the pan and top with a layer of the cream cheese frosting.

Step 19

Scoop little spoonfuls of curd all throughout the surface (you only need about 3/4 of the curd) and swirl into the frosting.

Step 20

Top with a sprinkle of poppy seeds and enjoy!