https://www.jeffreymorgenthaler.com/grapefruit-bitters/
Day One
1 fifth grain alcohol
3 grapefruits, peeled with a channel knife
1 lemon, peeled with a channel knife
1 tbsp. powdered gentian root
1 tbsp. minced ginger
1 tbsp. dried mint
1 tbsp whole cloves
Day Two
4 oz grapefruit juice
4 oz water
¼ tsp. vanilla extract
¼ tsp. almond extract
¼ tsp. coconut extract
Mix Day One ingredients and steep overnight
Add Day Two ingredients and strain the whole mixture through cheesecloth or coffee filters until clear.
In a large sauté pan, melt 6 oz (by volume) cane sugar until lightly caramelized. Add 6 oz water and stir until syrup is smooth and clear.
Add to alcohol mixture (away from the heat!) and bottle.