Combine the flour, baking powder, salt, and sugar in a large mixing bowl. Add the butter and rub it lightly with your fingertips to incorporate it into the flour.Gradually mix in the beaten egg and milk to make a thick batter. Set aside.Generously butter a 2 litre (8 cups) glass or ceramic bowl (that will fit into your 5-6 quart pot). Spoon in 4 Tbsp of the golden syrup and swirl around the bottom of the basin. Spoon the batter mixture into the prepared bowl.Place a 16-inch square of parchment paper on top of a 16-inch square of foil. Place the two sheets paper-side down onto the bowl and cover tightly.The foil should completely cover the bowl. Place a flameproof trivet into the base of your pot.Place the bowl of pudding on top of the trivet and fill it with water so that it reaches halfway up the sides of the bowl. Bring it to the boil over high heat for 30 minutes.Place the pot into your Wonderbag and seal for 2-3 hours until risen and springy to touch.Unwrap and carefully invert onto a plate, drizzle with an extra 4 Tbsp of syrup to taste.Serve with ice cream or custard on top.Pro tip: this dessert is best eaten as soon as it is cooked.NotesYou can easily make the golden syrup by melting 8 tbsp of sugar until caramelised.