Preheat the oven to 350F. Lightly butter a casserole dish. Cut an \"x\" into the root end of each Brussels sprout. Drop into boiling, salted water and cook for 5 min. Drain and refresh in ice water. Melt butter in a sauté pan and cook shallots for few min, until soft. Add Brussels sprouts and syrup and cook over medium heat until well glazed, about 3-5 min. Remove from the heat, add the zest, thyme, and nuts, and bake in the casserole dish for 15 min, or until tender and heated through.