Heat oven to 180C/160C fan/gas 4. Line the base of a 21cm square tin with baking parchment. Put the cocoa, butter and sugar in your largest saucepan and gently melt, stirring so the mixture doesn’t catch. When the cocoa mixture is melted and combined, cool slightly, then stir in the eggs, little by little, followed by the flour and coconut.
Tip into the tin and bake for 45 mins on a middle shelf - check after 30 mins and cover with another piece of baking parchment if the crust is browning too much. Cool in the tin, then carefully lift out and cut into squares.