Preheat the oven: Set oven to 350°F (175°C). Line two baking sheets with parchment paper.
Cream butter and sugars: In a large mixing bowl, beat butter, granulated sugar, and brown sugar together until light and fluffy (about 2 minutes).
Add wet ingredients: Mix in egg and vanilla extract until combined.
Mix dry ingredients: In a separate bowl, whisk flour, sea salt, and baking soda.
Combine: Gradually add dry ingredients to the wet mixture, stirring until just combined.
Fold in mix-ins: Gently stir in chocolate chips and Halloween sprinkles.
Scoop dough: Using a cookie scoop or spoon, drop dough balls onto prepared sheets, spacing 2 inches apart.
Bake: Bake 10–12 minutes, until edges are set and centers look slightly underdone.
Cool and enjoy: Let cookies rest 5 minutes on the sheet before transferring to a wire rack.