In a traditional way, dulce de leche was made in a copper pot, but we will use a normal casserole. Heat the milk with the sugar over medium heat, so that it dissolves. Add the bicarbonate and vanilla and stir. Vanilla can be used in the form of extract, essence or seeds, whatever we have, in the desired amount to give a little aroma.
Let the mixture cook for about two hours, stirring from time to time with a wooden spoon so that it does not stick, over a rather low heat, it should not boil. The water in milk it will evaporate, the liquid will decrease and we will notice how, little by little, it thickens and takes on color.
The time is a bit indicative, according to the fire of each one. The last hour is the most delicate since the dulce de leche is thicker and We must not stop stirring to avoid lumps or sticking to the bottom of the pan.
Remove from heat when we get a consistency similar to that of a custard. Out of the fire we keep stirring for 5 or 10 more minutes so that the dulce de leche cools down a bit. We will notice how it still thickens and reduces a little more. We pour into jars and store, either sterilizing or refrigerating, as we prefer.