1. Add the butter and sugar to a large bowl and mix until light and fluffy. Add the egg and vanilla extract and mix until well combined. Mix the flour with cornstarch, baking soda, and salt and add to the bowl – mix until just combined. Add the sugar-coated chocolate and fold in. Cover the bowl and place in the fridge overnight.

 

3. Preheat the oven to 350°F (180°C). Line a baking sheet with baking parchment. Divide the dough into 10 equal portions and place five of them with enough space in between on the baking sheet – keep the rest in the fridge. Bake the first batch of cookies for about 12 minutes until lightly browned. They will look quite underbaked, but that is ok. Take out of the oven and let cool down on the baking sheet for about 10 minutes, then transfer to a wire rack to cool down. Repeat with the second batch of dough.