Warm flavors such as cumin, cinnamon, cardamon, ginger, nutmeg, and allspice pair nicely with butternut squash. You can experiment with some of these spices if you choose by adding them to your curry, but don't go overboard! I would select one or two additional spices and add no more than a quarter teaspoon. Taste, and adjust the spices as needed. Other spices that pair nicely with butternut squash include more herbal flavors such as thyme, rosemary, and sage. With this particular curry, I would suggest sticking with warm spices, as they pair nicely with the yellow curry.