Preheat oven to 160C (fan forced) and line 4 large baking trays with baking paper.
Beat butter and castor sugar together in an electric mixture until pale and fluffy.
Add eggs one at a time beating well each time.
Add vanilla essence and whisk to combine.
Remove bowl from electric mixer and add sifted flour, baking powder, bicarbonate of soda, oats and peanuts. Stir until all ingredients are well combined.
Roll or squeeze 1 heaped teaspoon of cookie dough into balls (slightly smaller than a rum ball) and place on baking trays. Space the cookies to allow for spreading as they cook. Flatten each cookie gently with a fork.
Bake cookies for approximately 14 minutes or until just browned. Remove from oven and leave to stand of baking trays for approximately 5 minutes before transferring to a wire rack to cool completely.
Recipe by Mrs Organised at http://www.mrsorganised.com.au/2015/03/10/peanut-oat-cookies-one-recipe-75-cookies/