In a medium saucepan, combine sugar, water, a cinnamon stick, and a lemon peel. Bring to a boil over medium heat and cook for 5 minutes without stirring. Remove from heat and set aside to cool.

In a mixing bowl, whisk together milk, egg yolks, and cornstarch until smooth. Set aside.

In a pot, add the remaining milk, along with sugar and vanilla powder. Heat until hot and steamy but not boiling.

Slowly pour the hot milk into the egg yolk mixture while whisking constantly. Return the mixture back to the pot and cook over low heat, whisking until thickened.

Remove custard from heat, transfer into a bowl, and cover with plastic wrap. Let cool.

Preheat oven to 340°F (170°C). Grease a baking pan with butter.

In a large bowl, combine coarse and fine semolina, and baking powder. Mix well.

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

Add semolina mixture to wet ingredients and stir until combined.

Pour batter into the prepared pan and let rest for 30 minutes.

Bake for 20-25 minutes until golden-orange. Remove from the oven.

Immediately pour the cold syrup over the hot cake. Let it absorb for a few moments.

Allow the cake to cool to room temperature.

Beat heavy cream with sugar until thick and firm peaks form.

Once cooled, beat the custard until smooth and gently fold in whipped cream.

Spread the cream mixture evenly over the cooled cake and dust with ground cinnamon. Refrigerate for 6-8 hours before serving.