Preheat oven 180°C fan forced. Line 3 large baking trays with baking paper.
Using an electric mixer, beat butter, peanut butter, sugars and vanilla in a small bowl until smooth. Add egg, beat until combined. Transfer to a large bowl. Stir in flour and baking powder.
Roll leveled tablespoons of mixture into balls. Place about 3cm apart on prepared trays. Using your palm, flatten slightly. Press peanuts into the top of each biscuit. Bake two trays for about 12 minutes, or until golden around the edges. Cool on trays. Repeat with remaining tray.