Preheat oven to 150˚C (300˚F). Line 2 baking sheets with parchment paper. In large bowl, mix together the flour and cornstarch. Set aside.
In another bowl, use a wooden spoon to cream together the butter and sugar. Mix in mint extract and food colouring. Gradually stir in the flour mixture to make a soft dough. Using rounded tablespoons of dough, roll each spoonful into a ball (aim for walnut-sized). Place on lined baking sheets about 2 in. (5 cm) apart. Make 30 balls.
Chop the 1/3 chocolate-nougat bar into 30 pieces. Lightly press a piece onto the top of each dough ball, without flattening the dough.
Bake about 18 min., or until cookies are firm and bottoms are lightly golden. Cool on baking sheet. Store in airtight container 2 to 3 days.
Baked and cooled cookies can be layered between waxed paper or plastic wrap in airtight container and frozen up to 1 month. Or wrap the dough tightly in plastic wrap, seal in freezer bag and freeze up to 1 month. Thaw before proceeding with rolling, topping and baking cookies as per recipe.