Preheat your oven to 180 C / 350 F . Line a cookie sheet with parchment paper or grease well.
Chop up your chocolate into small bits and keep aside.
In a bowl, whisk together the flour , malt powder ( bournvita ) , baking soda and salt. Keep aside.
In a mixing bowl , using a electric beater or wooden spoon , beat together the butter and sugar until light and fluffy.
Add the yolks and beat well until incorporated .
Beat in the vanilla .
Add the dry ingredient mixture and mix until a dough forms.
Mix in the chocolate chips. Scrape up all the bits sticking to your chopping surface and mix it in too for the tiny flecks of chocolate !
Divide the dough into balls ( about a tablespoon full of cookie dough each ) . You should be able to make 28 to 30 balls.
Place the dough balls on the prepared sheet , well spaced out as they will expand ! You will need to bake the cookies in batches.
Bake at 180 C / 350 F for 16 to 18 minutes. If using a convection oven , take out the cookie sheet after 10 minutes and put it back in the other way round ( earlier front side towards the back now ).
Remove from oven and let cool on the sheet itself for about 5 minutes and then transfer to cooling rack to cool completely !