Put milk, sugar and vanilla bean paste (or vanilla bean pod and seeds) in a large sauce pan over medium heat and bring to a simmer stirring occasionally.

When sugar completely dissolves, add baking soda and salt. Reduce to low heat and cook for 3 ½ to 4 hours uncovered, stirring occasionally. If using vanilla bean pod and seeds, you’ll need to remove the pod after cooking for an hour.

Skim off foam as necessary (if there is too much).

In the last hour of cooking, stir the mixture frequently and reduce heat to the lowest setting if necessary, the mixture will bubble more rapidly.

Reduce the mixture to about 1 ½ cups. When it thickens and the color is caramel brown, it is ready.

Transfer to a jar and let cool to room temperature.

Preheat oven to 425°F.

Pour condensed milk into a pie dish, sprinkle salt over the top. Cover with foil.

Place covered pie dish into a roasting pan. Fill the pan with hot water half way up the side of the pie dish. Bake for 1 hour.

Remove roasting pan from the oven, and remove pie dish from the water bath. Uncover the dish carefully and whisk the mixture until smooth, 1 – 2 minutes.

Cover the dish and return to the water bath. Add more water if necessary. Place the roasting pan back into the oven and bake for 1 ½ hour more.

Remove from the oven, and remove pie dish from the water bath. Uncover and whisk the dulce de leche until smooth, 4 – 5 minutes.

Transfer to a jar and let cool to room temperature.