
Chocolate bitters are high-proof cocktail bitters flavoured with cacao and aromatic botanicals, dashed into drinks to season them — much the same as cocoa bitters.
Roasted cacao and dark chocolate lead, over aromatic spice and a dry, unsweetened bitterness on the finish.
A few dashes lend chocolate character and a bitter backbone, building complexity and balancing sweet and sour without adding volume. It shines with brown spirits — a couple of dashes lift a Manhattan, Old Fashioned or Negroni.
Another aromatic cocktail bitters covers the general bitterness; cocoa bitters is the closest match for the chocolate note itself. When a drink is built around that cacao character, though, nothing unrelated truly stands in.
Chocolate liqueur / crème de cacao
Chocolate bitters are high-proof and essentially unsweetened, dosed in dashes. A chocolate liqueur (crème de cacao) is sweet and lower-proof, poured in ounce measures as a base or modifier.
Cacao is macerated with herbs, barks and roots in a high-proof spirit base — which is both solvent and preservative — then cut with water. Like all cocktail bitters, it's a concentrated flavouring, not a drink you pour by the glass.

Chocolate Negroni
London dry gin

Banana Martini
Vodka

Eggs-cellent
Advocaat liqueur, Cognac

Bruised Pomegranate
Rye whiskey, Byrrh

Cubano
Caribbean aged rum, Amaro, Cherry liqueur

Double Black
Cacao & coffee spiced rum, Crème de Café liqueur

Jäger Old-Fashioned
German amaro (e.g., Jägermeister)

Top Banana
Light gold rum

Mexican Nail
Tequila reposado