Make the syrup: Combine sugar, water, lemon juice, cinnamon stick, and lemon zest in a saucepan. Bring to a boil, stir until sugar dissolves, simmer 5 minutes. Cool completely. Remove cinnamon and zest. The syrup must be cold before use.

Make the custard: Heat milk until steaming. Whisk eggs, sugar, semolina, and lemon zest in a large bowl. Slowly pour half the hot milk into the egg mixture while whisking constantly (tempering). Return to saucepan with remaining milk. Cook over medium heat, stirring constantly, 8-12 minutes until thick. Remove from heat; stir in butter and vanilla. Cover surface with plastic wrap to prevent a skin forming.

Preheat oven to 180 degrees C (350 degrees F). Butter a 9x13 inch (23x33 cm) baking pan.

Layer bottom filo: Place 6-7 filo sheets in the pan, brushing each layer generously with melted butter. Allow edges to overhang the sides of the pan.

Add custard: Pour the custard evenly over the filo base.

Layer top filo: Fold overhanging edges over the custard. Add remaining filo sheets, brushing each with butter. Tuck edges down inside the pan.

Score: Cut through the top filo layers (not into the custard) in serving portions - squares or diamonds.

Bake 45-50 minutes until deep golden brown all over. Rest 15-20 minutes out of the oven.

Add syrup: Pour the cold syrup slowly and evenly over the warm pastry. Let absorb 30-45 minutes at room temperature before serving.