Prepare the Lemon Custard: In a saucepan, combine the egg, sugar, and cornstarch until smooth.

Mix in the lemon juice, grated lemon peel, and milk.

Cook over medium heat, stirring constantly until the mixture thickens. Once thick, set aside to cool.

Make the Cake Dough: Preheat your oven to 190°C (374°F).

In a large bowl, whisk together the eggs, sugar, and vanilla sugar until well combined.

Gradually add the seed oil and milk, continuing to whisk.

Sift in the flour and baking powder and mix until the batter is smooth.

Bake the Cake: Pour half of the dough into a greased baking pan and bake in the preheated oven for 15 minutes.

Remove from oven, spread the lemon custard over the baked layer, then top with the remaining dough.

Return to oven and bake for an additional 25 minutes or until a toothpick inserted into the center comes out clean.

Add Toppings and Serve: Once the cake is baked, allow it to cool slightly.

Brush the top with your chosen jam and sprinkle with shredded coconut.

Let the cake cool completely before slicing to allow the flavors to meld together.