Line a metal square 8x8 baking pan with parchment paper on all four sides. Preheat the oven to 350 F/180 C.
Whisk together the flour, cocoa powder, espresso powder, and salt. Set aside.
Melt the chocolate chips and butter together until smooth.
In a large mixing bowl, whisk the brown sugar, granulated sugar, eggs, egg yolk, and vanilla extract until combined. Stream the melted butter and chocolate into the bowl, whisking constantly until just combined.
Fold the dry ingredients into the batter until just combined. Then pour the brownie batter into the prepared baking pan and sprinkle the almonds over the top. Bake for 33-40 minutes, or until a toothpick inserted into the center comes out covered in a few moist crumbs. In my oven, 35 minutes is perfect!
Take the pan out of the oven and cover the top with the mini marshmallows. Return the pan to the oven for about 2 minutes, until the marshmallows are puffy and lightly golden brown. You can also use a kitchen torch, which is my preferred way!
Remove the pan from the oven and let it cool completely on a wire rack. Once cool, drizzle with melted chocolate and sprinkle with more almonds and mini marshmallows if desired.
For clean cuts, liberally spray or oil a sharp knife. In between cuts, run the knife under hot water and wipe it clean. Re-oil it before the next cut. This will help keep the marshmallows from sticking to the knife!
Enjoy your rocky road brownies with a scoop of ice cream!