01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a large bowl, beat softened butter, granulated sugar, and brown sugar until light and fluffy, approximately 2-3 minutes.
03 - Beat in eggs one at a time until fully incorporated. Mix in vanilla extract.
04 - In a separate bowl, whisk together flour, cocoa powder, baking soda, and salt until well blended.
05 - Gradually add dry ingredients to wet mixture, mixing just until combined. Avoid overmixing to prevent tough cookies.
06 - Scoop 2-tablespoon mounds of dough onto prepared baking sheets, spacing about 2 inches apart to allow for spreading.
07 - Bake for 9-11 minutes until edges are set and centers appear slightly underbaked for fudgy texture.
08 - Let cookies rest on baking sheets for 5 minutes, then transfer to wire rack to cool completely.
09 - Place chocolate chips and butter in heatproof bowl. Heat heavy cream in small saucepan until just simmering, then pour over chocolate. Let stand 2 minutes, then stir until smooth and glossy. Cool 5-10 minutes until slightly thickened.
10 - Spread 1 tablespoon ganache over each cooled cookie. Immediately sprinkle with candy-coated chocolate chips while ganache is still tacky.
11 - Allow ganache to set at room temperature for approximately 20 minutes before serving. For faster setting, refrigerate briefly.