Stovetop Method (Most Traditional):

1. Combine the base ingredients: In a heavy-bottomed 4-quart saucepan, whisk together the whole milk, sugar, and baking soda until the sugar begins to dissolve. The mixture will foam slightly when you add the baking soda – this is normal.
2. Begin heating: Place the saucepan over medium heat and bring the mixture to a gentle simmer, stirring frequently with a wooden spoon to prevent scorching on the bottom. This should take about 8-10 minutes.
3. Reduce and monitor: Once simmering, reduce the heat to medium-low. You want a gentle, lazy bubble rather than a rolling boil. Cook for 1½ to 2 hours, stirring every 10-15 minutes at first, then more frequently (every 5 minutes) as it thickens.
4. Watch for color change: The mixture will gradually transform from white to cream to golden to deep amber. As it thickens, stir more constantly to prevent burning. The dulce de leche is ready when it’s reduced by about two-thirds, coats the back of a spoon, and has reached a rich caramel color.
5. Finish and strain: Remove from heat and stir in vanilla extract and salt. For ultra-smooth dulce de leche, strain through a fine-mesh sieve into a clean jar. Let cool to room temperature before sealing.

Oven Method (Hands-Off):

1. Preheat and prepare: Preheat your oven to 425°F (220°C). Pour the milk and sugar into a 9×13-inch baking dish and whisk in the baking soda.
2. Create water bath: Place the baking dish inside a larger roasting pan. Pour hot water into the roasting pan until it reaches halfway up the sides of the baking dish.
3. Cover and bake: Cover the baking dish tightly with aluminum foil. Bake for 1 hour, then remove the foil, whisk the mixture, and return to the oven uncovered.
4. Continue cooking: Bake for an additional 45-60 minutes, whisking every 15-20 minutes, until thickened and golden brown.
5. Cool and finish: Remove from oven and whisk in vanilla and salt. Blend with an immersion blender for 30 seconds for the smoothest texture. Cool and store.

Slow Cooker Method (Easiest):

1. Combine ingredients: Whisk milk, sugar, and baking soda in your slow cooker insert.
2. Cook low and slow: Cover and cook on LOW for 8-10 hours, whisking every 2 hours if possible. The longer it cooks, the darker and thicker it becomes.
3. Final steps: Once thickened and caramel-colored, whisk in vanilla and salt. Blend if desired for smoothness. Cool completely before storing.