In a large bowl, whisk together the melted butter and granulated sugar until well combined.
10 tablespoons unsalted butter, 1 cup granulated sugar
Whisk in the egg and vanilla and stir to combine.
1 large egg, 1 teaspoon pure vanilla extract
Add the flour, cocoa powder, and baking soda and stir until no large lumps remain.
1¼ cups all-purpose flour, ¼ cup unsweetened cocoa powder, 1 teaspoon baking soda
Gently fold in the chocolate chips and puffed rice-- you don’t want to smush the rice.
¼ cup chocolate chips, ½ cup puffed rice
Transfer the dough to the fridge to chill for 30 minutes.
While it is cooling, preheat the oven to 350°F and line 2 baking sheets with parchment paper.
Scoop 2-tablespoon-sized cookie dough balls onto the baking sheets about 2 inches apart. Bake until the cookies are set around the edges, but still slightly soft in the center, about 12 minutes.
Allow the cookies to cool on the baking sheet-- they will set as they cool. Then, transfer the cooled cookies to an airtight container.