Prepare the pan. Use the teaspoon of butter to rub and grease a 33 x 23 cm ( 13 x 9 inches) pan. Combine both types of semolina in a bowl along with the baking powder.
Prepare the cake batter. In a mixing bowl whisk together the Greek yogurt, milk, sugar, vanilla, lemon zest, baking soda, and Mastiha powder (if using Mastic tears see note 3 below). Add the dry ingredients to the wet ingredients and stir well until uniform.
Rest the batter. Transfer the batter to the prepared pan. Let it sit at room temperature for 30 minutes to thicken. Meanwhile, preheat the oven.
Preheat oven to 340°F / 170°C.
Bake the cake for about 20-25 minutes or until deep golden-orange on top.
Add the syrup. Ladle the cold syrup over the cake right as it comes out of the oven. The cake needs to be very hot to absorb the syrup properly.
Cool the cake down to room temperature.