Preheat the oven to 350°F and line two baking sheets with parchment paper or silicone mats.

Microwave the butter in a large microwave-safe bowl for about 40 seconds until mostly melted.

Whisk the butter until it is fully melted.

Combine the sugars with the melted butter and mix until well-blended.

Add the vanilla and egg to the mixture and stir until fully incorporated.

Mix in the dry ingredients: flour, cocoa powder, baking soda, and salt. Make sure to measure the flour correctly as noted in the recipe.

Mix the dough until just combined. The dough should be soft and slightly sticky, but not overly so.

Fold in the chocolate chips, mini marshmallows, and sliced almonds.

Scoop out the dough using a medium cookie scoop (about 1.5 tablespoons) and place them 2 inches apart on the baking sheets.

Bake the cookies for 7-10 minutes, or until they are set. They will appear puffy and slightly underbaked in the center.