- Portion size 40 servings
In bowl, beat butter with sugar until fluffy. Beat in cornstarch; stir in flour. Gather into ball; flatten into disk. Wrap and refrigerate for 1 hour.
Between waxed paper, roll out dough to 1/4-inch (5 mm) thickness. Using 2- or 3-inch (5 or 8 cm) decorative cookie cutter, cut out shapes. Freeze on parchment paper–lined rimless baking sheets for 10 minutes or until firm.
Bake in top and bottom thirds of 275°F (140°C) oven, rotating and switching pans halfway through, until firm to the touch and bottoms are light golden, 40 to 50 minutes. Let cool on pans on racks for 10 minutes; transfer to racks and let cool completely.
Icing Paint: Whisk sugar with water until spreadable, adding more water if necessary. Divide among small bowls; tint with colouring as desired. Using palette or small knife, spread thin coat on cookies. Let dry about 4 hours. Meanwhile, scoop remaining icing into separate resealable plastic bags; seal and set aside.
Snip small opening off corner of each icing bag. Pipe patterns onto cookies. Let dry, about 4 hours.