
According the information, Harmen Baer from Winschoten, maker's mark HB, in monogram.
I have my doubts. A monogram is a design consisting of two or more letters, often initials, combined or overlapping. It seems to me that we're looking at two separate initials here, but I'll check for you. Also his mark, what kind of cartouche, round, square or rectangle?
The length and weight are typical for a 17th-century spoon; the apostle is "scary" Paul with a sword, indeed a Groningen spoon.
Peter.