Heat half a liter of milk and pour in a pinch of salt and semolina, stirring constantly, and let it boil until it has a firm consistency. Then remove the pot from the stove.
In a second bowl, mix the eggs, sugar and the grated lemon zest together well and add the rest of the cold milk.
Slowly mix the contents of the second bowl with the cooked semolina. Put everything in a buttered ovenproof bowl or gratin dish. Sprinkle with flakes of butter and bake in a preheated oven at 150 ° C for 35 - 45 minutes.