Preheat the oven to 175 C (350 F)
In a large bowl, beat the butter and sugar until pale and light; add the egg and vanilla and beat until well blended and smooth.
In a small bowl, stir together the flour, baking powder and salt. Add half to the butter mixture, beating on low speed just to combine. Beat in the milk and then the remaining flour mixture, beating on low speed until well blended.
Pour into a parchment-lined 9x9-inch pan and bake for 25-30 minutes, until golden and springy to the touch. Let cool completely.
When you’re ready to coat the cake, cut it into 9 squares. To make the chocolate ganache, heat the cream until steaming; pour over the chocolate chips in a bowl and let sit for a minute, then whisk until smooth adding more cream if mixture is too thick to dip.
Place the coconut in a shallow dish. Dip each square into the warmed ganache to coat, then dunk it into the coconut to coat all over. Transfer to a tray or wire rack to set.