In the bowl of a heavy-duty mixer or in a medium bowl using a hand held mixer, cream the butter and sugar together until the mixture is pale and creamy, about 5 minutes. Add the eggs, a little at a time, beating well after each addition. Stir in the crystallized ginger. Fold in a few spoonfuls of the sifted flour into the bowl, alternating with spoonfuls of the milk, until both ingredients are used up and you have a smooth batter. Divide the pudding among the basins.
Quarter a sheet of parchment paper and fold a thin pleat down the middle of each mini-sheet. Place a piece over each basin and tie them down with string. Place the puddings in a steamer over a saucepan of gently simmering water and steam for 40 minutes or until the puddings are cooked through. Check the water level in the saucepan from time to time, adding more as needed. Switch off the heat and serve the puddings with the coconut custard and a sprinkling of crystallized ginger.