Grease and line a loaf tin with baking or parchment paper.
In a large mixing bowl, sift together flour, cocoa, baking soda and baking powder. Add sugars, pinch of salt and gently stir.
Use the microwave function on high for 30 seconds to melt the peanut butter. Place the butter in a large heatproof bowl. Microwave first for 30 seconds, give a stir then microwave for a further 20 seconds. Add the vanilla, eggs and milk and whisk until combined.
Preheat convection to 160°C and place the wire rack on the lower shelf position.
Make a well in the middle of your dry ingredients, add wet ingredients and gently stir the mixture using a spatula until just combined. Add most of chocolate chips to the batter and fold through.
Pour mixture into prepared tin, dollop the peanut butter on top and using a butter knife, swirl it into the cake mixture. Sprinkle the remaining chocolate chips on top. Bake for 60 minutes.
Cool in tin for 5 minutes, then transfer to a wire rack to cool completely.