Preheat your oven to 170℃ fan bake. Cream together 190g of softened butter and the caster sugar until light and fluffy.
Add the flour, cocoa powder and a pinch of salt then gently mix until a soft dough forms.
Roll the mixture into 20-24 balls, then lay onto lined baking trays. Use a fork to flatten slightly, then place into the oven and bake for 15 minutes.
While the biscuits are baking, make the filling by creaming the remaining butter and peanut butter together. Add the icing sugar and beat until fluffy in texture.
Once the biscuits have cooled, pipe or spread the peanut butter filling onto half of the biscuits, then sandwich with another. Enjoy or store in an airtight container.