In a large saucepan whisk together the milk, cream, C&H® Organic Raw Cane Sugar, vanilla bean seeds + pod, salt and bring to a boil.
Reduce to a simmer, whisk in the baking soda and set a timer for 1 hour.
Whenever you walk by the pot, give it a stir and adjust the temperature to keep it from boiling; you just want some bubbles around the edges of the pan. Usually between the 30-45 minute mark, the color starts to deepen and the mixture begins to thicken a bit. When this happens, it’s going to be more prone to a heavy boil (which is bad), so stay near it, adjusting the temperature as necessary and stirring more frequently. It should be done anywhere between 1 hour to 1 1/2 hours. This dulce deepens and thickens faster than usual because of the addition of cream, so keep an eye on it. You want the dulce to have a nice thick consistency as well as a bronzed and deep caramel appearance.
Strain the dulce into a heat-safe bowl. Pour into a lidded container and stash in the fridge until ready to use. It will thicken more as it cools.
Preheat the oven to 350°F (177°C). Grease an 8 x 11–inch (20.3 x 28–cm) baking dish and line with parchment paper, letting the excess fall over the sides.
In a medium, heat-safe bowl add the chocolate, C&H® Organic Raw Cane Sugar, C&H® Dark Brown Sugar, butter, and oil and set over a medium saucepan of simmering water. Do not let the bowl touch the water or let the water come to a boil. Stir frequently until melted and smooth.
Place a towel on the counter and set the bowl on top of it.
Whisk in the eggs, one at a time, making sure each is well blended before adding in the next.
Add in the vanilla, cocoa powder, and salt and stir to combine.
Fold in the flour to the chocolate mixture until just combined. Pour the batter into the prepared baking dish.
Place big drops of dulce de leche (with about ⅓ cup) over the top of the brownies, about 1-2 inches apart. Grab a knife and press it just beneath the surface of the brownies and make dulce swirls over the top of the brownies. *You will have extra dulce to serve; reserve remaining dulce for another use.
Bake on the middle rack of the oven for 25 minutes.
When done, they will have a bit of jiggle in the middle, and if you test with a toothpick, some batter will coat it. This is a good thing.
Let them cool in the pan for several hours and if you want extra fudgy brownies (and for them to be easier to cut), put them in the fridge for several hours before serving. Serve with any remaining dulce to drizzle over the top!
When it’s time to cut the brownies, use a very sharp knife, cut straight up and down and use a wet paper towel to clean off the knife in between cuts.