In a mixing bowl, sieve and add all-purpose flour, cornstarch, baking soda, and salt.
In another bowl, cream the sugar and oil until the sugar dissolves. Add vanilla extract and mix until smooth.
Now add the flour mixture to this in three parts, stirring well until just combined after each addition.
Crush Ferrero rocher chocolates in a grinder. You can even hand-chop them. Add this to the mixing bowl.
Mix and add some milk if required to get the desired cookie dough consistency.
Preheat the oven to 350° F. Line a cookie tray with parchment paper and place tablespoon-sized balls of dough evenly onto the prepared baking sheet.
You don't need to flatten them. They will spread.
Bake for 15-20 minutes. When done, the cookies would have spread a little and the edges would turn golden brown.
Just remember, every oven is different. So please use personal judgment and adjust the baking time as you think appropriate.
Take it out from the oven and allow it to cool for a couple of minutes before you start gorging upon them. They will also harden as they cool.
Always move them from the cookie tray to a cooling rack, else they will continue to bake if they stay in the hot tray.
Store in airtight containers and enjoy!