Dulce de leche is a combination of milk and sugar that has been slowly cooked until the sugars caramelize, producing a thick, creamy, intensely flavored spread. A simple, safe way to make it is by baking sweetened condensed milk in a water bath (no need to constantly monitor the stove or worry about scorching sugar). Dulce de leche is extremely versatile and can be used as an ice cream topping, a dip for fresh fruits, or the filling in Alfajores cookies.
1Heat the oven to 425°F and arrange a rack in the middle.
2Pour milk into a pie plate and sprinkle with salt. Cover tightly with aluminum foil and place in a roasting pan. Place the roasting pan in the oven and add enough hot tap water to reach halfway up the sides of the pie plate. Bake for 1 hour.
3Remove the roasting pan from the oven and remove the pie plate. Carefully uncover the plate and whisk the mixture until smooth, about 1 minute. Replace the foil and return the pie plate to the water in the roasting pan. Place back in the oven, adding more hot water so that it remains halfway up the sides of the pie plate. Continue to bake until the dulce de leche is dark golden brown (about the color of peanut butter), about 1 1/2 hours more.
4Remove from the oven and transfer the pie plate to a wire rack. Remove the foil and whisk the dulce de leche until smooth, about 3 minutes. Let cool to room temperature, then refrigerate in an airtight container with a tightfitting lid for up to 1 week.