Place blackberries and Everclear in to a sealable jars. This is the flavor jar.
Place gentian root, quassia chips, sarsaparilla root, cinnamon stick and 1 ½ cups 100+ proof rye or bourbon in to a seperate sealable jar. This is the bitters jar.
Let each sit for 2 weeks, shaking daily.
After 2 weeks strain out bitters jar through a fine-mesh sieve and then strain the rest through a coffee filter into the flavor jar after removing half of the blackberries.
Shake this new mixture with everything in one jar and let it sit for 10 days or more. Shake daily.
After this 10+ days, strain out remaining blackberries through a fine-mesh sieve, and then strain the rest through a coffee filter into your desired container(s).