Preheat your oven to 350°F (175°C). Grease a 13x9-inch baking dish.
In a large mixing bowl, whisk together melted butter and cocoa until well combined.
Add granulated sugar and eggs to the mixture, beating with a hand mixer until light and fluffy.
Gradually incorporate flour, salt, nuts, and vanilla, mixing until just combined.
Pour the batter into the prepared baking dish and bake for about 25 minutes.
When done, remove from the oven and immediately sprinkle mini marshmallows on top.
While the marshmallows melt, prepare the frosting by mixing softened butter, cocoa powder, and powdered sugar until creamy. Gradually add milk until smooth.
Spread the frosting over the melted marshmallows once the cake has cooled slightly.
Allow the cake to cool completely before cutting into squares to serve.
Send me this recipe!
Just enter your email below and get it sent straight to your inbox!
Notes
Store leftovers in an airtight container at room temperature for up to three days or refrigerate for up to a week.