In a mixing bowl, add the caster sugar, brown sugar and soften butter, and beat well to get a smooth texture.
Add the egg and beat again.
Add the peanut butter, and beat again for a further 30 seconds.
Sift in the flour and baking powder, and use a spatula to bring everything together into a small dough.
Leave the dough to rest for 5-10 minutes.
Preheat the oven to 180 degrees Celsius (350 Fahrenheit).
Line 2 large baking trays with non-stick paper.
With wet hands, scoop out dough to shape a ball of 25 g (0.8 oz).
Repeat with the rest of the dough.
Use a fork to press down on each ball to flatten it to a half a cm thickness.
Top each cookie with 4 or 5 peanuts, then bake for 15 minutes or until golden.
Remove from the oven, and leave them to cool for 5-10 minutes before arranging them on a cooling rack.