Grease and line two 8 inch / 20cm round cake tins and lightly dust with some flour, then set aside. Or use cooking spray to grease the tins.
add buttermilk, water, oil, sugar, eggs, baking soda / bicarbonate of soda and salt in a bowl and whisk or use a handheld beater to mix together until it is well combined. Add in flour and cocoa powder and mix until smooth and there are no lumps.
Divide the batter evenly into greased pans
Bake at 350°F / 180°C for 20-25 minutes until a skewer inserted comes out clean or until you can lightly touch the center and it springs back.
Cool the cakes in the pan on a wire rack for 10 minutes, then remove cake and allow to completely.
If the cake formed a dome during baking then cut it off to form a level surface. Do this only once the cake has cooled completely.
Sandwich the cake layers, the top and sides with the peanut butter frosting. Place in the fridge while you make the chocolate ganache. SEE NOTE 2
Pour the cooled and thickened ganache over the cake and allow to drip onto the sides. Place the cake in the fridge and let it chill until the ganache is set.
Decorate the top of the cake as you prefer ( I used whole and halved chocolate covered peanuts)