Make and refrigerate sugar cookie dough according to recipe instructions (or use store-bought dough).

Roll chilled dough to 1/4 inch thick on a lightly floured surface.

Using a ruler to create straight edges, cut the dough into rectangles approximately 3 inches x 4 inches.

Place the rectangles 2 inches apart on a baking sheet lined with parchment paper. Bake at 375° for 10-12 minutes, until edges are just starting to turn lightly golden brown.

Transfer to a wire cooling rack to cool completely.

Make the icing by combining powdered sugar, milk, vanilla extract, and green food coloring in a small bowl and mixing until smooth.

Ice the cookies and add green sugar sprinkles. Let dry completely.

Add the marshmallows, cut side down.

Decorate with black gel icing. Cool completely.