Gather all of your ingredients and equipment before you get started. 

Preheat the oven to 350°F and line baking sheets with parchment paper.

Measure all of the ingredients before you begin. In a medium bowl, whisk together the flour, baking soda, baking powder, and salt.

In a large mixing bowl, beat the softened butter with the granulated sugar and brown sugar until light and fluffy, about 2 to 3 minutes.

Add the egg, egg yolk, and vanilla extract, mixing until smooth and well combined.

Lightly crush the cornflakes with your hands, leaving plenty of larger pieces for texture.

Gradually add the dry ingredients to the butter mixture, mixing just until no dry flour remains.

Fold in the crushed cornflakes and white chocolate chips, being careful not to overmix so the cereal keeps some of its crunch. If using, gently A technique used to gently mix two ingredients together to create a light fluffy consistency. Start by scooping around the outside of the bowl and cutting through the centre. Turn the bowl and repeat the process.fold in the toasted coconut.

Using a cookie scoop or tablespoon, portion the dough into balls about 2 tablespoons in size and place them on the prepared baking sheets, leaving about 2 inches between each cookie. If desired, sprinkle the tops with a pinch of flaky sea salt.

Bake for 10 to 12 minutes, or until the edges are lightly golden and the centres still look slightly soft.

Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a cooling rack to cool completely.