Delicious condensed milk and quick cooking.
These are products that we need, as you can see they are few, but they must be fresh :-). Powdered sugar is better to buy, because it contains starch, which contributes to thickening ;-).
Take a pan with high walls (milk at boiling rises and can escape), pour the milk, add the butter and sifted icing sugar.
Put on low heat and stir until the butter and powder is dissolved. Then swap on average (!!!) fire and bring to a boil, once it boils, stirring constantly cook for 10 (!!!) minutes.
Pour into a jar, wait until cooled, and even better to leave overnight in the fridge:) the Condensed milk might seem watery, but when cooled it thickens.