Pre heat oven to 350°. Lightly grease, or line with non-stick foil, a 9” x 13” brownie or cake pan.
Place the dark chocolate, unsalted butter, and espresso powder in a large microwave safe bowl. Heat in 30 second intervals, stirring after each just until the chocolate is fully melted. Whisk in the sugar, brown sugar, salt, and vanilla. Whisk in the eggs until well combined. Stir in the flour and cocoa powder just until the flour disappears. Fold in the chopped snickers.
Spoon ½ the batter into the prepared pan, smooth out to the edges in an even layer. Drizzle the peanut caramel over the batter leaving about ½” around the perimeter of the pan. Spoon the remaining batter over the top of the caramel, gently smoothing to completely cover the caramel.
Place the pan in the pre-heated oven and bake for about 30-35 minutes. The top will appear set, the brownies may wiggle slightly due to the melted caramel layer. Allow to cool while making the nougat.