Preheat the oven to 350º

Line an 8" pan with foil, and grease with butter.

Whisk the flour and espresso together in a medium mixing bowl.

Place the butter pieces face down in a medium sauce pan on very low heat. A little OCD, but it works.

When the butter is nearly melted, add the chocolate. Whisk well until the chocolate is melted.

Remove from the heat, add the cocoa, and whisk until smooth.

Add the eggs, one at a time, whisking well each time.

Stir in the sugar, vanilla, and flour mixture.

Use a spatula to thoroughly mix the batter, scraping down the sides and make sure no dry ingredients are on the bottom.

Pour half of the batter into the baking pan. Using a small offset spatula, smooth the surface of the batter.

Drop 9 tablespoons of the dulce de leche onto the batter. Using a butter knife, swirl through the batter.

Pour the remaining batter into the pan. Smooth the surface.

Repeat the 9 tablespoons of dulce de leche and leave as is, or swirl as preferred.

Bake for 25-30 minutes, until the top is slightly jiggly. Do not overbake, or the batter will turn out dry. Unless you like your brownies cakie rather than fudgy.

Remove from the oven, sprinkle with Maldon salt, let cool for 30 minutes.

Once cool, lift the brownies out of the pan. Plate to serve, or refrigerate for 24 hours for better texture. If you can wait.