Oh the things we learn. After I’ve already recorded several verses always pronouncing blessed as “blest” in every situation, it turns out I should have indeed said, “bless-ed.” To me, “bless-ed” sounded more King James-ey and archaic and thus needing to be modernized. Nope. So “blest” is the verb way of saying it and “bless-ed” is the adjective (or even sometimes the noun) way of saying it.
He blest the bless-ed one!