Place all the syrup ingredients into a small saucepan, bring to the boil and reduce until thick and sticky. Set aside to cool.
In another saucepan, bring the semolina, sugar, vanilla and milk to the boil, stirring constantly over medium heat to form a thick custard. This can take up to 15 minutes.
Remove from heat, cooling slightly, then whisk in the eggs, a small amount at a time.
Preheat the oven to 180°C.
Prepare the filo pastry by laying one sheet on a flat surface, brush with melted butter, cover with another sheet of filo pastry and repeat the process until you have eight layers. Cover the unused filo with a damp tea towel to avoid drying it out.
Line the base of a 20 x 20cm square cake tin with the prepared filo pastry then pour in the cooled custard.
Brush and layer another 8 sheets of filo pastry and place over the custard, folding and tucking the pastry edges. Make a few small cuts in the top pastry to allow steam to escape.
Bake for 40 minutes or until lightly golden and puffed. Gently pour the cooled glaze evenly across the top while the custard slice is still hot, then sprinkle with ground cinnamon. Allow to cool completely in the tin before cutting.
Galaktoboureko is best served at room temperature.
