Cream butter and both sugars on medium speed until smooth. Add egg and beat on high 1 minute. Add vanilla and molasses; mix well.
In a separate bowl, toss oats, flour, cinnamon, baking soda, and salt together. Add to wet ingredients and mix on low until combined. Fold in white chocolate chips and macadamia nuts. Dough will be thick. Chill 25–30 minutes.
Preheat oven to 325°F. Line two baking sheets with parchment.
Roll dough into 1.5-tbsp balls and place 2 inches apart. Bake 10–11 minutes until very lightly browned on the sides. Centers will look soft.
Cool on baking sheet 5 minutes before transferring to a rack.