Step 1: Preheat the oven to 350°F (175°C).
Step 2: Cream together the cold butter and brown sugar until light and fluffy.
Step 3: Add eggs one at a time, then mix in peanut butter and vanilla extract.
Step 4: In another bowl, whisk together flour, cornstarch, salt, baking soda, and baking powder.
Step 5: Gradually add dry ingredients to the wet ingredients, mixing until just combined.
Step 6: Fold in white chocolate chips and chopped candies using a spatula.
Step 7: Scoop dough onto baking sheets, spacing them 2 inches apart.
Step 8: Bake for 10-12 minutes until edges are golden and centers are soft.
Step 9: Let cookies cool on baking sheets for 5 minutes before transferring to a cooling rack.
