Melt Butter: Melt butter in a small saucepan over low heat, stirring occasionally. Alternatively, melt in the microwave in 30-second intervals.
Cool the Butter: Pour melted butter into a medium size mixing bowl and set aside to cool for 5 until it’s only slightly warm. Ensure it doesn’t firm back up.
Mix Sugars: Add both sugars to the melted butter and whisk until well combined, about 20 seconds.
Add Yolk & Vanilla: Add the egg yolk and vanilla extract, whisking until well combined.
Add Dry Ingredients: Add the flour, cornstarch, baking soda, and salt. Mix with a spatula until a soft, smooth dough forms and no streaks of flour remain.
Fold in Chocolate Chips: Fold through the chocolate chips.
Chill Dough: Cover and refrigerate the dough for 30 minutes.
Preheat Oven: Preheat the oven to 356°F (180°C). Line a small baking sheet with parchment paper and set aside.
Shape Cookies: Roll the dough into 2 large cookies (approx. 45g-50g each) or 3 smaller cookies. Place on the lined baking sheet without flattening the balls.
Bake: Bake for 7–9 minutes or until the edges are lightly golden and the centres look slightly soft.
Cool: Let the cookies cool on the baking sheet for 15 minutes, then transfer to a wire rack to cool completely. Enjoy!