Layer 5 sheets of phyllo in the bottom of the pan, brushing each sheet generously with melted butter, making sure to get the butter all the way to the edges. Once done, cover the pan and remaining phyllo sheets with a damp towel to keep them from drying out.

You can make the custard first and cover it with plastic wrap to prevent a skin from forming, then prepare the phyllo.

For the custard:

In a saucepan, combine the milk, semolina, and sugar. Heat over low, stirring until the mixture is hot but not boiling. In a separate bowl, beat the eggs.

Add the citrus zest and vanilla to the milk mixture in the saucepan. Gradually add the beaten eggs, stirring constantly, until the custard thickens. Once thickened, remove from heat and stir in the 3 tablespoons of butter until fully incorporated.
Now preheat your oven to 340°F (170°C) for conventional or 320°F (160°C) for convection.

Layer the remaining phyllo sheets on top of the custard, brushing each with butter. This time, tuck the edges down along the sides of the dessert, pressing them gently to the bottom if possible. I use the butter brush to help tuck them in—it works great.

Once all the phyllo is in place, cut the dessert into pieces as desired, brush the top well with butter, and sprinkle water over the top with your hand to moisten evenly. Bake in the preheated oven at 340°F (170°C) (or 320°F/160°C for convection) on the middle rack for at least 1 hour, until golden brown and the phyllo is dry and crisp.