Lemon Sponge Cake with Lemon Cream Filling

Preheat your oven to 180°C (350°F). Grease and line a 23 cm (9-inch) round cake pan with parchment paper.
In a large mixing bowl, beat the sugar and lemon zest together until fragrant.
Add the eggs, one at a time, beating well after each addition.
Sift together the flour and baking powder, then fold them into the egg mixture, stirring gently until just combined.
Pour the batter into the prepared cake pan and smooth the top.
Bake for 25-30 minutes, or until a toothpick inserted into the center of the cake comes out clean.
Allow the cake to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely (about 1 hour).
Prepare the Lemon Cream Filling:

In a saucepan, whisk together the sugar, cornstarch, and egg until smooth.
Gradually add the lemon juice and milk, stirring to combine.
Place the saucepan over medium heat and cook, stirring constantly, until the mixture thickens to a custard-like consistency (about 5-7 minutes).
Remove from heat and stir in a pinch of turmeric for color and the softened butter. Mix until the butter is completely incorporated and the cream is smooth.
Let the cream cool to room temperature, then refrigerate for at least 30 minutes to allow it to set and become firm.
Assemble the Cake:

Once the cake has cooled, slice it in half horizontally to create two layers.
Spread a generous amount of the lemon cream filling over the bottom layer of the cake.
Place the top layer of the cake on top and gently press it down.
Serve:

You can optionally dust the top of the cake with powdered sugar or garnish with fresh lemon zest before serving.
Tips:
For an extra burst of flavor, you can add a little lemon extract to the cream filling.
If you want to enhance the color of the cake, you can add a few drops of yellow food coloring to the cream filling.
This cake pairs well with a cup of tea or fresh berries for added freshness.