Wash and slice the navel orange and place it in a sealable glass jar. Do not remove peel. Add bitter orange peel, then pour in the gin and vermouth. Seal and shake the jar, then steep at room temperature for a minimum of 24 hours and up to 72 hours.

Strain the orange out with a sieve and then filter through cheesecloth or a coffee filter into glass bottle or jar. Store sealed at room temperature.