1Combine the rhubarb, ¼ cup (1¾ oz) superfine sugar and the water in a medium saucepan over medium-low heat. Bring to a simmer and cook for 5 minutes until the rhubarb is just tender. Strain the rhubarb, discarding the liquid.
2Put the egg yolks, milk, vanilla and butter in a medium bowl and whisk until well combined.
3Combine the pudding powder, flour, baking powder and remaining ½ cup (3½ oz) superfine sugar in a large bowl and make a well in the center.
4Whisk the egg mixture into the flour mixture to form a smooth batter. Fold in half of the rhubarb.
5Beat the egg whites with a stand mixer until stiff peaks form. Gently fold the egg whites into the batter.
6Select BELGIAN waffle setting and dial up 6 on LIGHT/DARK indicator dial.
7Preheat until the orange light flashes and the word HEATING disappears.
8Pour ½ cup of the batter into each waffle square. Close the lid and cook.
9Repeat with the remaining batter.
10Serve waffles with vanilla pudding and remaining rhubarb, dusted with powdered sugar.