Dulce de Leche

Instructions

1. 1 In a large, heavy-bottomed, deep saucepan (at least 4-quart capacity), combine the whole milk and sugar. Place over medium heat and stir gently with a wooden spoon until the sugar dissolves completely, about 3-4 minutes. The pot must be deep because the mixture will foam dramatically in the next step, and a shallow pan will cause it to boil over.
2. 2 Dissolve the baking soda in 1 tablespoon of warm water, then add it to the milk mixture. The baking soda will cause the milk to foam up vigorously — this is normal and expected. Stir to subside the foam. The baking soda serves two critical purposes: it neutralizes the lactic acid in the milk to prevent curdling during the long cooking process, and it accelerates the Mailvegetable shortening browning reaction that gives dulce de leche its signature golden caramel color.
3. 3 Add the cinnamon stick if using, then bring the mixture to a gentle boil over medium heat. Immediately reduce the heat to the lowest possible setting so the liquid barely simmers with only occasional small bubbles breaking the surface. This low-and-slow approach is essential — high heat will cause the milk to scorch on the bottom and develop a bitter, burnt taste.
4. 4 Cook the mixture at this bare simmer for 1 1/2 to 2 hours, stirring every 10-15 minutes during the first hour, then every 5 minutes during the final hour as the mixture thickens and becomes more prone to scorching. As the water slowly evaporates, the dulce de leche will progressively deepen from white to golden to a rich amber-caramel color. Scrape the bottom and corners of the pot with each stir to prevent sticking.
5. 5 The dulce de leche is ready when it has reduced to about one-third of its original volume, turned a deep golden-brown color, and coats the back of the wooden spoon thickly. To test the consistency, drop a small amount onto a cold plate — it should hold its shape without spreading. Remove from heat, stir in the vanilla extract, and discard the cinnamon stick. Remember that dulce de leche will thicken significantly as it cools.
6. 6 Pour the hot dulce de leche through a fine-mesh strainer into clean glass jars to catch any small lumps or the cinnamon stick residue. Allow to cool to room temperature with the lid off, then seal and refrigerate. The dulce de leche will keep for up to one month in the refrigerator. Use it to fill alfajores, spread on toast, layer in cakes, drizzle over ice cream, or eat straight from the jar with a spoon — as any proper Argentine would.