Beat the butter in a large mixing bowl until smooth and creamy.
Add the granulated sugar, brown sugar, honey, cinnamon, and salt. Beat until pale and fluffy.
Add egg and vanilla, mixing until blended. Begin adding the flour, working it in a cup or two at a time, mostly to avoid it spilling over the edge of the bowl.
Divide the dough into two pieces, then flatten into disks and refrigerate. You'll need at least an hour, but overnight works well too.
When it's time to bake, preheat the oven to 350 F.
Prepare at least 2 cookie sheets by lining with parchment paper.
Dust a clean countertop and rolling pin with flour. Working with one disk at a time, roll it out to 1/4 inch thick, then cut out cookies with a 2 inch cutter. Transfer to the prepared baking sheets. Ball up and re-roll the unused dough to make as many cookies as you can. They won't spread while baking, but give them about a half inch or an inch of space between them.
Because these cookies are so small and thin, they're very delicate in the oven. Bake one rack at a time, and pay attention to how they brown. We had the best luck with darker metal cookie sheets. With those, we baked them for 10 minutes, then transferred them to a cooling rack right out of the oven. On lighter metal trays, they needed about 2 minutes longer in the oven, and it helped to have them rest on the cookie tray about 5 minutes before transferring to the cooling rack.
Let the cookies cool completely before adding the filling.
Blueberry Pie Filling
Mix butter with an electric mixer until smooth and creamy. Work in powdered sugar about 1/2 cup or 1 cup at a time. It'll get crumbly, but keep at it. Add the vanilla and blueberry extracts, then mix again.
Eyeball the texture. It's probably still somewhat crumbly. Add the tablespoon of heavy cream and whip. Hopefully it'll be as creamy as you'd like, but if not, add another tablespoon and keep mixing.
To frost the cookies, you've got a couple of options. A piping bag would work the prettiest, but we found another good technique. Put a dollop of frosting in the center of one cookie, then gently put the second cookie on top of the frosting. Push the top cookie down while twisting in a single direction. That'll help push the frosting out to the edges, without spilling out unevenly.
It's a big batch, so be sure to enjoy with friends, or lots of milk.