For the Dulce De Leche Buttercream
In a large saucepan whisk together the milk, cream, sugar, vanilla bean seeds + pod 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 stick near it adjusting the temperature as necessary and stirring more frequently. It should be done anywhere between 1 hour and 15 minutes to 1 1/2 hours. This dulce deepens and thickens faster than usually 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.
Place the egg whites, sugar and sea salt in the bowl of an electric stand mixer and set on top of a pot of simmering water. Whisk constantly, for about 3-4 minutes or until the mixture is thick, opaque and when rubbed between two fingers no longer feels gritty. Place the bowl in the mixer fitted with the whisk attachment and whisk on high until it holds stiff peaks. Replace the whisk with the paddle attachment, and with the mixer on medium add the butter, one chunk at a time, waiting for one to blend completely before adding in the next. If the mixture curdles, your butter may be too cold. If it’s soupy, you may need to chill it for a quick spell in the fridge. Once all the butter has been added, run the machine for several more minutes until the mixture is smooth, glossy and voluminous. Run the machine on medium and add in 1/3 cup (75ml/104g) of the dulce de leche.
For the Cookie
Preheat the oven to 325F and line several baking sheets with parchment paper.
Place the hazelnuts in the bowl of a food processor fitted with the blade attachment and pulse until they are finely chopped and have the appearance of fine breadcrumbs. Add in the flour, cocoa powder, brown sugar, powdered sugar and sea salt and pulse until completely combined. Scatter the butter over the hazelnut mixture, along with the milk and vanilla and pulse to combine. Use a spatula to scrape the sides and bottom of the bowl to make sure everything is combined.
Form 1 teaspoon-size dough balls and place on the baking sheet, 1-inch from each other. Bake in the center of the oven for 10 minutes. Let cool on the baking sheet for 10 minutes before transferring to a rack to finish cooling.
Once cool, smear the bottom of one cookie with the dulce buttercream and set another cookie on top.
Thank you for making these cookies! Be sure to tag me @displacedhousewife #displacedhousewife #12DaysOfTreats so I can see your beautiful cookies!!
**This is the original version of this recipe; the one included in the Bake From Scratch issue has some quantity differences.