• Preheat the oven to 350°F and grease/line an 8x8 inch baking pan with parchment paper.
• Melt the semi-sweet chopped chocolate and butter in a double boiler by placing the chocolate and butter in a heat proof bowl over a pot of simmering water on medium-low heat. Melt by stirring with a spatula occasionally until the butter and chocolate is fully melted, ribbony and smooth.
• Turn-off the stove, remove the bowl, and wipe any condensation/moisture from the bottom of the bowl. Then, immediately while whisking, stream in the granulated sugar. Whisk until the sugar is fully dissolved into the butter/chocolate mixture. 
• Whisk the eggs in one at a time. Making sure each egg is fully whisked in before adding the next. Beat batter longer after eggs are incorporated for a shiny crinkly top. The mixture should now be thick and fall in glossy ribbons.
• Whisk in vanilla extract, instant espresso powder, and dutch process cocoa powder until fully combined. Fold in all-purpose flour, salt, and chopped walnuts until just combined and no streaks of flour can be seen. 

to assemble

• Pour half of the brownie batter into the prepared pan, then pour 1/2 cup of caramel sauce into the center spreading evenly with a spatula leaving a 1 inch border empty (this prevents the caramel from leaking when baking). Lastly, top with the remaining half of the brownie mixture. 
• Bake for 25-30minutes until the brownies are baked through, but still fudgy, there should be a couple crumbs clinging to an inserted toothpick. Do not over bake, the center should be slightly wet. Remove from the oven and let cool for at least 20 minutes in the fridge, or until the pan can be handled, before removing from the pan and cutting into 16 two inch squares. 
• For fully set brownies, chill them for at least 2 hours or overnight in the fridge before cutting.