Prepare Dough: Mix the butter and sugar in a large bowl until fluffy. Add the egg and vanilla extract, combining thoroughly. Roll out the dough to about 1/4 inch thick.

Cut Cookies: Use a small square cookie cutter to cut out cookie shapes from the rolled dough and place them on a parchment-lined baking sheet.

Bake Cookies: Preheat oven to 350°F (175°C). Bake for 4-5 minutes until edges are lightly golden. Keep an eye on them at the 4-minute mark.

Cool: Let the cookie bites cool on the baking sheet for about 2 minutes, then transfer them to a wire rack to cool completely.

Frosting Preparation: Beat softened butter until creamy, then gradually add powdered sugar and a splash of milk. Split frosting into three bowls, tint one red, another green.

Decorate: Spread frosting on each cookie and sprinkle on colorful decorations. Allow frosting to set for about 30 minutes.