Sift the flour then add to the sugar and peanut powder. (If using icing sugar, sift it with the flour.)
The amount of oil you will need varies depending on how much oil is produced after you've blended the nuts so add approximately 90% of the oil to the peanut powder, flour and sugar mixture first. Mix well. If the mixture is too dry, add the rest of the oil and mix till homogenous. (Too dry a dough won't hold together, and too wet a dough will ooze into a flat oblong puddle instead of keeping the round cookie shape.)
Use a ½ tablespoon scoop to scoop out the dough then roll each scoop into a round ball. The cookies don't spread much in the oven and may be placed very close to each other on the baking mat.
Take out the peanuts that you've separated into halves earlier and press half into the centre of each cookie.
Use a brush to brush the egg yolk wash over each cookie, diluting slightly with water if it is too thick.
Bake at 350F/ 176C till golden brown (approximately 17-20 minutes) Turn the baking tray around halfway through baking for a more consistent colour (as ovens have hot spots, usually at the back corners)
Allow to cool then enjoy these crunchy yet melt in the mouth snacks!