In a large mixing bowl or the bowl of a stand mixer, combine butter, brown sugar, white sugar, salt, and 2 teaspoons of vanilla. Using a stand mixer or hand-held mixer, beat the mixture until it becomes smooth and creamy. Scraping down the sides a couple of times will ensure everything is well combined.
Add in the flour and water, mixing until just combined. You'll want to see a soft dough forming. Be careful not to over-mix, as this can lead to tougher cookies.
Next, stir in the chopped pecans. This is where you'll start to see the texture of your cookies come together. The pecans will add that wonderful crunch, so be generous with your stirring!
Now, place the dough onto a large piece of parchment paper or plastic wrap. Using your hands, shape the dough into a log that’s about 10 inches long and 2 inches in diameter. This will create the shape of your cookies when sliced.
Wrap the dough tightly and chill it in the freezer for 30 minutes or in the fridge for 2 to 3 hours. Chilling is crucial as it helps the cookies hold their shape while baking.
While the dough chills, it’s time to caramelize the sweetened condensed milk. Pour it into a non-stick saucepan and simmer over low heat for 20 to 30 minutes, stirring often to prevent burning. You’re looking for a light caramel color; this will give your cookies a sweet filling.
Once your caramel is done, stir in 1 teaspoon of vanilla and remove it from the heat. Allow it to cool slightly while you prepare the cookies.
When you’re ready, preheat your oven to 350 degrees Fahrenheit and line a baking sheet with parchment paper.
Unwrap the chilled dough log and place it on a cutting board. Using a sharp knife, cut the log into 1/4 inch slices. Carefully arrange the slices about 1 inch apart on the prepared baking sheet. This gives them room to spread while baking.
Bake the cookies for 10 to 14 minutes, until their edges turn a nice golden brown. Keep a close eye on them; you want them perfectly baked.
Once out of the oven, allow the cookies to cool completely. This step is essential for the next part.
Once cooled, spread the bottom half of each cookie with the caramelized sweetened condensed milk. It’s thick, so be gentle as you spread it on. If it’s too thick, you can warm it slightly over low heat to make it easier to work with.
Add the top cookie to form a sandwich and place all sandwich cookies on a parchment-lined baking sheet.
Now it’s time to melt your chocolate. You can do this over a double boiler or in the microwave, stirring every 30 seconds until it’s smooth and melted.
Drizzle the melted chocolate over each cookie. If you want an extra touch, sprinkle with flaky sea salt before the chocolate sets. To firm up the chocolate, place the tray of cookies in the fridge for 5 minutes.
Finally, store your cookies in an airtight container for up to 4 days at room temperature, if they last that long!
