Sweet and citrusy Golden cane-sugar syrup infuses this steamed pudding topped with a blood-orange sauce and candied zest.
Make the pudding: Set a round wire rack in the bottom of a large stockpot. Set a 5-cup pudding basin or ovenproof bowl on rack. Fill pot with enough water to come about three-quarters of the way up sides of basin. Remove basin; dry, and butter inside. Set aside. Cover pot, and bring to a boil.
Butter a 10-inch round of parchment paper; set aside. Pour golden syrup into prepared basin. Add 1 teaspoon orange zest and the orange juice; set basin aside. Whisk flour, baking powder, and salt in a medium bowl; set aside.
Put sugar and remaining teaspoon zest into the bowl of an electric mixer fitted with the paddle attachment. Mix on medium-high speed 30 seconds. Add butter; mix until pale and fluffy, about 2 minutes. Add eggs, one at a time, mixing well after each addition (mixture will look curdled). Add flour mixture in 2 additions, alternating with milk, and mix until combined.
Pour pudding into prepared basin. Place parchment round, buttered side down, over basin. Make a pleat in center of parchment. Cover with an 11-inch round of foil. Make a pleat in center of foil to allow room for pudding to expand. Cut a piece of kitchen twine about 7 feet long. Wrap twine twice around basin over foil, just below lip. Knot to secure. Tie loose ends to twine on other side of basin, creating a handle.
Carefully lower pudding into boiling water; cover pot. Return to a boil; reduce to a simmer, and steam until an instant-read thermometer inserted into center of pudding registers 180 degrees, about 1 1/2 hours, adding boiling water occasionally to maintain level.
Meanwhile, make the candied zest if desired: Using a paring knife, peel oranges, trying not to get any white pith with the skin. Slice into very thin threads. Heat sugar and 1 cup water in a small saucepan over medium heat, stirring to dissolve sugar. Add zest, and simmer until tender and translucent, about 25 minutes. Let cool completely in syrup.
Meanwhile, make the sauce: Put golden syrup, orange juice, lemon juice, and salt into a small saucepan. Bring to a boil over medium-high heat. Reduce heat to medium-low, and simmer until thick and syrupy, about 7 minutes.
Transfer pudding to a wire rack. Let cool 10 minutes. Run a knife around edge of bowl to loosen, and invert onto a plate. Serve warm with sauce, and garnish with candied zest if desired.