Just to clarify, the "black bean paste" used to make Hoisin sauce is NOT the same as the black beans you find in cans for Mexican cooking etc.

Chinese "black bean paste" is actually fermented soybeans -- they have a very unique flavour and are not in any way similar to what most North Americans think of as "black beans".

"Black bean paste" can be found in jars in Asian groceries and often in the Asian section of grocery stores as well.

If you do not have Chinese "black bean paste" do not use regular black beans instead -- you would be terribly disappointed in the taste. You're far better off either buying prepared Hoisin sauce at the grocery or using peanut butter or tahini instead (I'd suggest a tad more dark vinegar to achieve the fermented taste of the orginal).