Make the Syrup:
In a saucepan, combine sugar, water, cinnamon stick, and lemon peel. Bring to a boil and cook for 5 minutes without stirring. Set aside to cool completely.

Prepare the Custard Cream:
In a bowl whisk ½ cup milk, egg yolks, and cornstarch until smooth.

Heat the remaining milk in a pot with sugar and vanilla until hot and steamy.

Temper the Eggs:
Slowly add the hot milk to the egg mixture while whisking constantly. Once about two-thirds is incorporated, pour everything back into the pot.

Thicken the Custard:
Cook on low heat while whisking until the mixture thickens into a creamy custard.

Transfer the custard to a bowl, whisk to smooth it, and cover with plastic wrap touching the surface. Let cool to about 20°C / 68°F.

Prepare the Cake Batter:
Grease a 33 × 23 cm (13 × 9 inch) pan with butter.

In a bowl mix coarse and fine semolina with baking powder.

In another bowl whisk yogurt, milk, sugar, vanilla, lemon zest, baking soda, and mastiha powder.

Add the semolina mixture to the wet ingredients and stir until fully combined.

Pour the batter into the prepared pan and let it rest 30 minutes while the oven preheats.

Preheat oven to 340°F (170°C).

Bake the cake for 20–25 minutes until golden-orange on top.

Add the Syrup:
Immediately pour the cold syrup over the hot cake.

Allow the cake to cool to room temperature.

Make the Whipped Cream:
Beat the heavy cream with sugar using an electric mixer until thick and firm.

Cream the Custard:
Beat the cooled custard until smooth and soft.

Combine the Creams:
Gently fold the whipped cream into the custard in two batches until fully incorporated.

Spread the cream mixture evenly over the cooled cake.

Dust the top with ground cinnamon.

Refrigerate for 6–8 hours before serving.

Cut into 12 square pieces and serve chilled.