Put the sugar, butter and Nutella in a large bowl. Whisk until combined and fluffy.
Add the eggs, milk and vanilla and beat until creamy.
Add the flour and oats. Mix until well combined. It’s easiest to use a silicone spatula for this, so that you can scrape down the sides as you go.
Divide the mix into 12 balls. They’ll weigh about 100g (3.5 oz) each.
Flatten the balls and place a Ferrero Rocher in the centre. Roll the cookie dough back around the Ferrero Rocher to form a ball again. Place them well-spaced on a baking sheet lined with baking paper. You don't need to flatten them.
Bake for 15 minutes per batch until set and a little cracked.
Allow to cool on the tray for a few minutes to firm up, then transfer to a wire rack to cool completely.
Place the white chocolate in a small, microwave-safe bowl. Microwave in 30-second bursts, stirring between bursts until melted smooth.
Add gold lustre and mix until evenly coloured.
Drizzle the white chocolate in zig zags all over the cookies. You can do this either with a spoon, or by transferring the chocolate to a small piping bag and snipping off the very end.
Once these cookies have cooled and the white chocolate frosting has set, you can simply transfer them into an airtight container or reusable zip lock bag.They are best kept somewhere out of direct sunlight in a cool spot, so in the pantry or cupboard would be perfect.When stored in the cupboard in an airtight container, these cookies will keep for 5-7 days.