Preheat the Oven to 180C/160C Fan, and line 2-3 large baking trays with parchment paper.
In a bowl, whisk together the plain flour, malt powder, bicarbonate of soda, salt, and cornflour. This just distributes all the ingredients evenly.
Melt your butter carefully and then add to a bowl. Add the two sugars. Whisk for two minutes with an electric whisk (or three minutes by hand)
Add in the egg and whisk again briefly to combine.
Add in the dry Ingredients, and beat until a cookie dough is formed.
Add in the Malteser Buttons (or chopped Teaser bar) and Maltesers, and combine - I just do this with my hand and a spatula.
Using a 5-6cm ice cream/cupcake/cookie scoop, scoop your mixture. The mixture can be larger than the scoop, but it gives you a general idea of how to make them consistently sized.
I made 15 cookies out of mine, as I made them quite large. Press any leftover bits of chocolate from the bowl into the top of the cookies.
You want to make sure there is only about 6 cookies for a 40cm long tray for example, so that when they spread in baking, they don't touch.
Bake the cookies in the oven for 11-13 minutes, and then leave to cool on the tray for 15 minutes before transferring to a wire rack. Enjoy!
These cookies will last up to five days, if not eaten already.
If you can't access the Malteser Buttons, you can use the Malteser chocolate bar, chopped up. If you can't access that, you can use more Maltesers, but I'd use normal chocolate chips instead. .
The cookies are naturally thick and not meant to spread - if you want them a bit flatter, pat the mixture down a bit.