Step 1: Prepare the Dough

1. In a large mixing bowl, combine the melted butter, granulated sugar, and light brown sugar. Whisk until smooth and creamy.
2. Add the eggs and vanilla extract, mixing until fully incorporated.
3. In a separate bowl, whisk together the flour, cornstarch, cocoa powder, baking soda, and salt. Gradually add the dry ingredients to the wet mixture, stirring until a thick dough forms.
4. Cover the bowl with plastic wrap and refrigerate the dough for 30 minutes to ensure thick, chewy cookies.

Step 2: Bake the Cookies

1. Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.
2. Using a cookie scoop or tablespoon, portion the dough into 2-tablespoon-sized balls. Place them on the baking sheets, spacing them 2 inches apart.
3. Slightly flatten each dough ball with the back of a spoon or your fingers.
4. Bake for 8–10 minutes, or until the edges are set but the centers remain soft.
5. Let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.

Step 3: Make the Ganache

1. Chop the chocolate into small pieces and place them in a heatproof bowl.
2. Heat the heavy cream in a saucepan over medium heat until it begins to steam (avoid boiling). Pour the hot cream over the chocolate and let it sit for 2–3 minutes.
3. Stir the mixture until smooth and glossy. Add the vanilla extract and mix well.

Step 4: Frost and Decorate

1. Once the cookies have cooled completely, use a spoon or offset spatula to spread a generous layer of ganache over each cookie.
2. Sprinkle the ganache with Cosmic Brownie sprinkles while it’s still wet.
3. Let the cookies sit at room temperature for 15–20 minutes to allow the ganache to set before serving.