where does one buy speculoos butter in washington, dc area?

Have to agree with Trader Joe's "Cookie Butter", but if you aren't near a TJ's, it is actually a rather common find - Lotus Bakeries (the Belgian originator of the well-known Biscoff brand of speculoos cookies) makes Biscoff Spread in both smooth and crunchy varieties. Target definitely sells this brand, but I recall seeing it at Giant and Harris Teeter in the DMV as well.

Trader Joe's!

trader joe's usually has it! it may be marketed as "cookie butter."

It's simple to make it at home, if you're up for it! Recipe here: https://food52.com/recipes/33547-speculoos-cookie-butter

Or Trader Joe's sells a good one!