Into a pan, add the milk powder, the refined sugar and the water, mix very well with the heat still off until it reaches a creamy consistency.
Add 10ml of water and stir over low heat. Stir for 15 to 30 minutes nonstop to keep it from burning.
Once it's firm and coming off the pan, that's the right consistency.
Grease a baking tin with butter and pour the mixture while still hot, spread well.
Cut the dulce the leche into squares with a knife greased with butter (keep greasing it). Cut while still a bit hot.