This wonderfully simple dessert has uncertain origins! …the inhabitants of Sestino, in the province of Arezzo – known as “Sestinesi” – say that it’s one of their town’s oldest recipes, but the people from the Marche region (which isn’t far away) also claim it as their own. What is certain is that, in these areas, Bostrengo kept the wolf from the door for many generations. Higher up, in the mountains, they used to (and still do) substitute the wheat flour with chestnut flour; while in the Marche they used to add (and still do) honey, dried fruit, chestnut flour and a bit of whatever was in the pantry.
Turn the oven on, set it to 180 °C and put the milk on the stove to boil. Use a whisk to mix the eggs and sugar together, then add the flour and grated lemon rind. Gradually add the milk to the other ingredients, stirring until the mixture is a nice and creamy. Pour it into a buttered baking tin and put it in the oven for roughly 50-60 minutes. The liquid will thicken; “test” the consistency, from time to time, by sticking a toothpick into it. When it comes out dry, the Bostrengo will be cooked and have turned a lovely deep yellow, slightly caramelised here and there.