For the cookies, melt the chocolate and butter together in a large bowl in a microwave or double boiler; cool slightly. Whisk in the sugar, egg, and vanilla. Stir in the flour, cocoa powder, baking powder, and salt (the batter will be soft). Cover the bowl with plastic wrap and put it in the freezer until stiffened, about 15 to 20 minutes.
Preheat the oven to 350F and line a large baking sheet with parchment paper or silpant liners.
Use a 2-tablespoon scoop to measure out the dough. Roll into balls and arrange on the prepared baking sheet. Bake until the cookies are light golden on the bottom, but not firm in the center, about 8 to 10 minutes. Cool completely on the tray before removing.
Once the cookies are cool, make the buttercream. Use a handheld electric beater to mix the butter and jam together in a medium bowl. Add the powdered sugar and continue beating until smooth and creamy. (Depending on how thick your jam is, you may need a little more jam or powdered sugar to achieve the right consistency.)
Assemble the cookie sandwiches by sandwiching 2 cookies together with frosting in the middle.
Recipe by An Edible Mosaic™ at https://www.anediblemosaic.com/fudgy-dark-chocolate-cookie-sandwiches-with-raspberry-buttercream-for-two/