A shutter assembly, or other architectural structure or exterior/interior decorative trim element, having a foam insert at least partially enveloped by a cementitious shell. The assembly is molded from cementitious slurry, including gypsum cement and a latex/water mixture. An amount of the slurry is added onto a bottom mold surface portion to a desired depth and/or weight. The foam insert is provided with a plurality of spacer elements disposed in a surface thereof, which is placed atop the slurry in a desired orientation, whereupon an additional amount of the slurry is then added so as to at least partially envelop the foam core or insert. Engagement members on the top mold portion are then brought into contact with the spacer elements so that the foam insert remains at least partially submerged within the slurry. A top portion of the spacer elements can be removed from a base portion of the spacer element to reveal a bore formed in the base portion. The bore can receive a fastening or mounting member to facilitate painting or mounting of the shutter assembly. After sufficient curing, the shutter assembly is removed from the mold and is ready for immediate use and/or further processing.