Preheat oven to 350 degrees. In large bowl, cream butter and both sugars until well blended. Add egg and vanilla extract, and mix to combine.
In separate bowl, sift flour, baking soda and salt together. Slowly add dry ingredients into butter mixture and stir until combined.
Fold in candies and chill dough for 1 hour or overnight. Drop dough by rounded tablespoons onto lightly greased tray, about 2 inches apart.
Bake for 8-10 minutes for chewy cookies, or 12-14 minutes for crispy cookies.