Using a hand mixer or a stand mixer fitted with paddle attachment, cream the softened butter and both sugars together on medium speed until smooth. Add the egg and mix on high until combined, about 1 minute. Scrape down the sides and bottom of the bowl as needed. Add the vanilla and molasses and mix on high until combined. Set aside.

In a separate bowl, toss the oats, flour, cinnamon, baking soda, and salt together. Add to the wet ingredients and mix on low until combined. Fold in the white chocolate chips and macadamia nuts. Dough will be thick. Chill the dough for 25-30 minutes in the refrigerator.

Preheat oven to 325°F (163°C). Line two large baking sheets with parchment paper or silicone baking mats.

Roll balls of dough (about 1.5 tablespoons of dough per cookie—I like using this medium cookie scoop) and place 2 inches apart on the baking sheets. I pressed a few extra white chocolate chips/nuts into the tops of the cookies for looks. Bake for 10-11 minutes until very lightly browned on the sides. The centers will look very soft. Remove from the oven and let cool on baking sheet for 5 minutes before transferring to a wire rack to cool completely.