Sift the dry ingredients (flour, sugar, cornstarch, and cocoa powder if making chocolate cookies) together.

Prepare a pastry bag with a star decorating tip and line a baking sheet with parchment paper.

In a bowl, combine the margarine and powdered sugar.

Blend the margarine and sugar together with a rubber spatula.

Mix the ingredients using an electric hand mixer for about 4 to 5 minutes.

Preheat oven to 180C (350F).

Add the dry ingredients into the bowl with the wet ingredients.

Mix with the spatula using a cutting action until the mixture becomes crumbly.

Add milk and mix by rubbing against the bowl until the mixture is smooth and the crumbliness disappears.

Put the dough into the prepared pastry bag.

Pipe the dough into desired shapes onto the parchment-lined baking sheet.

If shaping like a rose, pipe the dough outward from the middle.

Bake for about 20 minutes, or until golden brown.

If the dough is too firm to pipe, massage it gently with your hand.

Let the cookies cool and serve.