Preheat oven to 170C (conventional) / 160C (convectional). Line 2 baking sheets with parchment paper / Silpat.
Place 40 grams of Nestum cereal on a baking sheet. Bake for 7 to 10 minutes until lightly golden and fragrant. Remove and let cool completely.
Whisk flour, cornstarch, salt, baking powder and baking soda in a small bowl together. Set aside.
In a large mixing bowl, add in the softened butter. Whisk until it is of toothpaste consistency. Whisk in the sifted icing sugar until fully incorporated. Whisk in egg and vanilla until fully incorporated.
Sift in the flour mixture. Use a spatula and mix until a batter is formed. Mix in the toasted Nestum, chia seeds and black sesame.
Scoop and roll approx 10 to 12 grams of batter into balls.
Coating and Baking
Sift the 10 grams of Nestum to remove the fine bits. Transfer into a small bowl. Place a cookie ball into the Nestum and toss to coat, pressing gently to form a slightly flattened disc. Transfer the cookie onto the baking sheet.
Repeat, spacing each cookie approx. 2.5-cm (1-inch) apart from one another.
Bake for 20 to 22 minutes until the cookies are golden-brown in colour. Place baking sheet on a wire rack and let the cookies cool completely before storing them in air-tight containers.
NOTES
If you don't have chia seeds, you can substitute it with white or black sesame seeds or simply omit them altogether.