Cream butter and both sugars until combined.
Combine flour, baking soda, and salt in a medium bowl. Stir and set aside.
Turn mixer on low. Add egg, mixing completely. Mix in vanilla extract. Add flour mixture to the wet ingredients and mix until combined. Add Kit Kats and white chocolate chips. NOTE: if you’re not using a stand mixer, chop your Kit Kats smaller. If you are using a stand mixer, run it on medium-low speed for about 15 seconds. The Kit Kats will break up smaller during mixing.
Important: Cover bowl with plastic wrap and chill dough for at least 2 hours. They taste best when baked from the refrigerator.
Preheat oven to 350°. Line cookie sheets with parchment or silpat liners.
Scoop out 2 tablespoon sized balls and place two inches apart on cookie sheet.
Bake for about 10-12 minutes. 10 minutes will be slightly underdone (the way I love them) but if you like a more done cookie, let them bake an extra minute or two. Let cool for 5 minutes, and then remove from pans to cool completely.