Mix butter, dill, garlic, lemon zest, cumin, salt, and ground black pepper in a bowl.
Cut cauliflower stem flush with the rest of the head so it can stay upright in a casserole dish. Spread butter mixture evenly over the top and sides of cauliflower, place in a casserole dish, and cover with foil.
Roast in the preheated oven until tender and cooked through, about 1 1/4 hours. Transfer to a platter and spoon any liquid in the casserole dish over the cauliflower.
