¼tspcoarse Kosher salt(if using table salt, use half the amount)
½cupsemi-sweet or dark chocolate chips
⅔cupunsweetened, Dutch-processed cocoa powder
⅓cupall-purpose flour,spooned and leveled
½tspcoarse Kosher salt(if using table salt, use half the amount)
2tspinstant espresso powder or instant coffee,optional
In a bowl, stir together the melted butter, sugar and brown sugar until smooth. Add the vanilla and egg yolk, and stir vigorously until smooth.
Separately, combine the flour, salt and baking soda. Add to the butter mixture, and stir to form a dough. Let cool for 10 minutes.
Stir in the chocolate chips; the dough will be stiffer now than it was before cooling. Scoop the dough into 9 balls and refrigerate the dough balls while you make the brownie batter.
In a large saucepan, melt the butter and sugar over medium heat. Once it begins to bubble, cook for two minutes. Remove from the heat and use a wooden spoon to stir in the chocolate chips and vanilla until melted and shiny; the mixture will be grainy. Let cool for 10 minutes.
Beat in the eggs, one at a time, until the mixture comes together into a smooth batter.
In a bowl, sift together the cocoa powder, flour, salt and espresso powder. Add the dry ingredients to the batter and mix just until no dry streaks remain. The batter will be thick but spreadable.
Assembly and Bake
Preheat the oven to 325 F. Line an 8 or 9-inch baking pan with parchment paper.
Spread the brownie batter evenly into the pan.
Smash the chilled cookie dough balls between your hands to flatten them a little, and arrange them on top of the brownie batter. Sprinkle the top with a few more chocolate chips.
Bake the brownies on the center oven rack for 28-30 minutes, until slightly puffed and set.
Cool the brownies completely (at least 6 hours or overnight) before cutting, if you want them to be set and slice cleanly when you cut them. You can speed up the cooling process by cooling them at room temperature for 1 hour, then refrigerating them for 1-2 hours.
Lift the cooled brownies out of the pan by the parchment paper onto a cutting board to cut them into servings. If you like, sprinkle the top of the brownies with coarse finishing salt.
Store leftover brownies in an airtight container at room temperature for up to 3 days. You can also wrap the brownies individually in plastic wrap and freeze for up to 3-6 months. Let thaw to room temperature for a quick treat.