In a large mixing bowl, combine melted butter, granulated sugar, and light brown sugar until smooth and creamy. Stir in egg and vanilla extract until fully combined.

In a separate bowl, whisk together flour, baking soda, and salt. Gradually add dry mixture to wet ingredients, stirring until just combined.

Fold in chocolate chips and Halloween sprinkles into the cookie dough without overworking it.

Form 2-tablespoon-sized balls of dough and place them on a parchment-lined baking sheet, spacing about 2 inches apart.

Cover the baking sheet with plastic wrap and refrigerate the dough for 1.5 to 2 hours.

Preheat the oven to 350℉ (175℃). Bake dough balls for 11-13 minutes until edges are golden and centers are set but slightly soft.

Immediately press candy eyes onto each cookie and allow them to cool on the baking sheet for 5 minutes before transferring to a wire rack.