Line a large plate or small baking tray that fits in your freezer with parchment paper. In a medium bowl, whisk together the flour, baking soda, and salt until evenly combined.
In a large mixing bowl, beat the softened butter, brown sugar, and granulated sugar until light and creamy, about 2 to 3 minutes. Add the egg and vanilla extract, then mix until smooth and fully incorporated.
Add the dry ingredients to the butter mixture and mix on low speed just until no dry streaks remain. Fold in the chocolate chips and candy-coated chocolate pieces until evenly distributed through the dough.
Cover the bowl and chill the dough for 30 minutes so it firms up enough for easy scooping.
Use a medium cookie scoop or spoon to portion the dough into 24 equal mounds. Place the portions on the prepared tray or plate in a single layer.
Freeze the dough portions until firm, about 30 minutes. Transfer the frozen dough balls to a freezer-safe container or zip-top freezer bag and return them to the freezer until needed.
When ready to bake, preheat the oven to 175 degrees Celsius. Line a baking sheet with parchment paper and place as many frozen dough portions on the sheet as needed, leaving space between them.
Bake the cookies directly from frozen for 12 minutes, or until the edges are lightly golden and the centers still look slightly soft. If desired, press a few extra candy-coated chocolate pieces onto the tops immediately after baking for a more festive finish.
Let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool further. Repeat with the remaining frozen dough portions as needed.