1. Preheat oven to 250°. Remove zest from oranges with a vegetable peeler and put zest on a baking sheet (save fruit for another use). Bake until zest dries, starts to curl up, and begins to brown, 20-25 minutes. Let cool.
2. Put all ingredients except sugar in a 1-qt. glass jar and seal tightly. Let sit in a cool, dark place for 2 weeks.
3. Strain liquid through cheesecloth into a 1 1/2- to 2-qt. glass jar and set aside. Put flavorings in a small saucepan with 2 cups water. Cover and bring to a boil, then reduce heat and simmer 10 minutes. Set aside.
4. Cook sugar in a small saucepan over medium-high heat, lifting and shaking pan occasionally, until sugar caramelizes and turns deep amber, 8-10 minutes. Pour caramel into liquid in pan (it will bubble furiously and may firm up).
5. Set pan in a bowl of ice water until liquid is cold, about 10 minutes. Pour into jar with first infusion. Seal and let stand in a dark place 5 days.
6. Strain final mixture through cheesecloth. Divide bitters into small jars and seal tightly.