In a medium sized saucepan add lemon juice, sugar, egg, and egg yolk. With a whisk, constantly whisk the curd, while heating it up on a medium heat until it starts to thicken.

Then take it off the heat, and pour it through a sieve over a bowl, to catch any cooked egg bits.

Let it sit for 2 minutes to slightly cool down. Then add the cold cubed butter and stir it in while it melts into the curd. Cover the curd with a piece of cling film so it touches the surface of the curd and place it in the fridge. Let it cool down until it’s needed.

For the crumble, add all of the ingredients to a bowl and mix it together, either by hand using a fork or with an electric mixer, until a crumble structure and there is no dry flour left. Set it aside while preparing the cake.

Preheat the oven at 175ºC/350ºF conventional oven and prepare a 23 cm/9-inch springform with parchment paper.

Sift together the all-purpose flour, baking powder and salt and set it aside.

In a large bowl, add lemon zest and granulated sugar, and rub it together to release all of the lemon zest flavor, until it looks like wet sand. Then add the butter and mix it on high speed using an electric hand mixer or a stand mixer, for 3 minutes.

Add the eggs one at a time into the mixture and on low speed mix it in until combined.

Continue by adding half the dry ingredients, on low speed, mixing until just combined.

Then add the lemon juice, sour cream, vegetable oil, vanilla extract and mix until just combined. Then add the other half of the dry ingredients and mix until combined.

Add the cake batter into the prepared cake pan and even it out. Then top it with the lemon curd, and spread into an even layer. Finally top it with the crumble.

Bake it for 45-50 minutes or until the cake tester comes out clean. Once baked, let the cake cool. After 10 minutes, gently drag a thin knife along the edge of the cake to release the cake from the springform. Let it cool down completely on a wire rack.

Stir together all of the ingredients until smooth. Drizzle it over the cake and it’s ready to be served.