My lady got my Parson's "Bitters" book for Christmas, and it has reawakened an interest/hunger to work on some bitters recipes.
"Abbott's Bitters" haven't been made for a long time, but Robert Hess @ DrinkBoy had posted a formula for a reasonable facsimile of Abbott's Bitters.
Here's the formula paraphrased.
4 tbsp gentian root
4 tbsp fresh ginger, peeled and sliced into quarter-sized disks
4 tbsp cardamom, whole
4 tbsp cassia
4 tbsp whole cloves
10 cups (2.36L, a little more than 3 750mL bottles) vodka or Everclear (grain alcohol)
1 cup sugar
1 cup boiling water
In 5 separate containers (preferably glass), mix one of each herb with 2 cups alcohol. These will form the "tinctures".
Let steep for 10 days, shaking once per day.
Strain each tincture through coffee filter paper, discard the solids, rinse with clean hot water, and return tincture to its container. (It will help to label them to keep track!)
Make caramel sugar syrum: heat sugar in pan until it melts and turns light brown (be careful, don't let it burn or turn too brown, it will continue to cook off-heat).
Remove from heat, and slowly stir in 1 cup of boiling water. Switch to a whisk to dissolve, and return to heat to dissolve, if necessary.
Next combine the following parts (start with teaspoon or 1/2 teaspoon measures):
1 part gentian tincture
1 part ginger tincture
6 parts cardamom tincture
8 parts cassia tincture
4 parts clove tincture
5 parts caramel sugar syrup
Combine in a bottle with dash top. Enjoy in your favorite cocktail!