Preheat the oven to 350 degrees F (175 degrees C).

Grease or line an 11×15-inch cookie sheet with parchment paper.

In a mixing bowl, cream together the butter or margarine and sugar until light and fluffy.

Add the egg yolk and vanilla extract, mixing well until fully incorporated.

Gradually add the flour to the butter mixture, stirring until a dough forms.

Press the dough evenly into the prepared cookie sheet.

You can use waxed paper to help flatten the dough with your hands or a rolling pin.

Bake in the preheated oven for 20 to 30 minutes, or until the shortbread is light golden brown.

While the shortbread is still warm, cut it into squares using a sharp knife.

Allow it to cool slightly in the pan.

To make the icing, mix together the confectioners’ sugar, softened butter, and boiling water until smooth and creamy.

Adjust the consistency by adding more water if needed.

Drizzle the icing over the warm shortbread squares.

Allow the shortbread to cool completely before serving.

Enjoy this classic Mother’s shortbread, a timeless treat perfect for any occasion!