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To make the cookies, start by mixing softened butter with powdered sugar until smooth. A hand whisk or a stand mixer with a paddle attachment works fine; the goal is to blend until creamy without overmixing. Next, add plain all-purpose flour and fold it into the sugar-butter mixture with a spatula until it resembles a crumbly, rough dough.
Once the dough comes together, use your hands to knead it into a smooth, cohesive ball. This simple process yields a versatile shortbread base perfect for customizing.