Ingredients: 

onion

 milk

flour

butter

salt

Melt butter and add salt and an onion crushed finely. Fry until the onion is golden brown. Add half a glass of milk. Stir the mix until the milk boils. In the meantime, prepare a mix with half a glass of milk and a couple of tablespoons of flour, add the cold-milk-with-flour to the boiling milk. Stir it, until the mix gets thick. Add a little bit of flour if necessary. Top the cannelloni with the thickened mixture, add Parmesan cheese and put the cannelloni inside the oven.