Add sugar, water, lemon juice, lemon peel, and cinnamon stick, if using, to a saucepan. Bring the mixture to a gentle boil and cook for approximately 5–7 minutes until slightly syrupy.
Pour the milk into a large saucepan and heat gently until warm, but do not allow it to boil.
In a separate bowl, whisk the eggs, sugar, semolina, vanilla, and lemon zest until well combined.
Slowly add some of the warm milk to the egg mixture while whisking continuously. This helps gently bring the eggs up to temperature.
Remove from the heat and stir in the butter. Allow the custard to cool slightly.
Preheat the oven to 180°C / 350°F.
Carefully place one sheet of phyllo into the dish, allowing some of it to extend over the edges. Brush generously with melted butter.
Pour the slightly cooled custard over the prepared phyllo layers.
Fold any overhanging phyllo over the custard. Continue layering the remaining phyllo sheets on top, brushing each sheet generously with melted butter.
Using a sharp knife, gently score the top phyllo layers into portions. Do not cut deeply into the custard.
Bake for approximately 50–60 minutes, or until the top is deeply golden and crisp.
Slowly pour the cool syrup over the hot pastry, allowing it to soak gradually between the layers.
Allow the dessert to rest for at least 1–2 hours before serving so the custard can set and the syrup can distribute evenly.