Put powdered sugar in the butter and knead until soft, add condensed milk, and beat with an egg beater.

Break apart the chocolate, place into a microwave safe container, and microwave for about 40 seconds until it melts.

Add Step 1 to 2 and mix, add the egg yolk and stir more until it thickens.

Sift in cake flour, and roughly mix. Cover your hand with a plastic bag and secure at the wrist with rubber bands, and mix until you can no longer see any flour.

Turn the bag from your other hand inside out and cover the dough with it, and let sit in the fridge for more than 10 minutes.

Stretch out the dough from the top of the bag, and cut open from the center. Cut into your desired shapes.

Make the smiley face using a straw. Carve out an ellipse with the straw for the mouth. If excess pieces get stuck, blow from the other side (the pieces will fly so be careful).

Fold the bag, stretch it out, and cut out shapes... Bake in an oven preheated to 355°F/180°C for 8 minutes.

Cut a marshmallow and sandwich it between the cookies (for a 45 mm cookie, cut the marshmallow into about 1/3).

Microwave for about 10 seconds while checking on it, and take it out once the top cookie has begun to rise (as if floating), and turn it off. Sandwich together firmly.