Preheat your oven to 180C/350F/Gas 4 and butter a 24x26cm/9½x10½in baking tin, 4-5cm/1½-2in deep.
Put the dates in a bowl, pour on 200ml/7fl oz of boiling water and stir in the bicarbonate of soda.
Cream the butter and sugar together in a large bowl until light and fluffy. Gradually add the beaten egg, beating well after each addition. Sift the flour and baking powder together over the mixture and fold in. Stir in the dates and their soaking water, then fold in the fudge pieces and 50g/1¾oz of the macadamia nuts.
Transfer the mixture to the prepared tin, spreading it evenly. Bake for 25-30 minutes, or until firm and springy to the touch.
Meanwhile, to make the toffee sauce, melt together the butter, sugar and cream in a saucepan over a low heat. Bring to the boil and let bubble for 3-4 minutes, or until the sauce is thick enough to coat the back of a wooden spoon.
Preheat your grill to high. Make holes all over the cooked pudding with a skewer. Pour half of the sauce over the pudding and place under the hot grill. Grill for 2-3 minutes, or until the sauce is bubbling. Keep your eye on it as it can burn easily.
Cut the hot pudding into portions and serve with the remaining warm toffee sauce, sprinkled with the remaining chopped nuts, and ice cream or cream.