Preheat the oven to 180C/350F/Gas 4, and line 2 baking trays with parchment paper. Set aside.
Roughly crush the cornflakes into smaller pieces, then stir in the malt powder, sugars, and salt. Add the melted butter and mix well.
Spread the cornflakes out into a thin layer onto one of the prepared baking trays, and bake for 10 - 15 minutes until crispy and golden. Let cool completely.
For the Cookies
Whisk together the flour, baking powder, cornflour, baking soda, and salt. Set aside.
Whisk together the butter and sugar until combined. Add the egg, egg yolk, and vanilla, and mix until combined.
Add the dry ingredients, and mix until just combined. Fold in the chocolate chips and cornflakes.
Roll the dough into 1.5oz balls, about 25 balls, place on the prepared baking tray, and press the extra chocolate chips on top. Bake for 10 - 12 minutes. Do not over-bake.
Allow to cool on the baking tray for 10 - 15 minutes before transferring to a wire rack to cool completely.
Once cooled, drizzle with melted chocolate if desired.
Notes
Cookies stay fresh covered at room temperature for up to 1 week. Cookie dough balls can be kept in the fridge for up to 5 days, or frozen for up to 3 months. Bake from frozen for an extra minute.