For the cookies: Preheat the oven to 375 degrees F. Cream the butter, cream cheese and sugar until smooth using a handheld mixer in a medium bowl. Add the flour slowly, mixing on low, until incorporated. Scoop the dough into a ball using your hands and cover with plastic wrap. Refrigerate until the dough has firmed slightly, about 30 minutes.

On a floured surface, roll the dough about 1/8-inch thick. Cut out as many rounds as possible with a small cookie cutter and transfer to ungreased baking sheets, leaving about 1 inch between each cookie. Re-roll the dough scraps and repeat until all the dough is used. Use a smaller cutter, about 3/4-inch, or cut freehand with a small sharp knife to punch a small window out of half of the cookies. Place the cutouts on the baking sheets and sprinkle all the cookies and cutouts with the colored sugars.

Bake until golden around the edges, 12 to 15 minutes. Cool for 5 minutes on the baking sheets and then transfer to wire racks to cool completely.

For the filling: Place the sugar, butter, mint extract, food coloring and 1/2 teaspoon of water in a medium bowl and beat on medium speed until well combined and fluffy. Spread a thin layer of mint filling on the cookies without the windows and place the wafers with the windows on top. Sprinkle with the confectioners' sugar, if using, and serve the sandwich cookies with the cutout cookies on the side.