In a large mixing bowl, add all of the filling ingredients, except the rhubarb.
Whisk the filling ingredients together, until well mixed.
Pour the filling into the baked crust and let settle.
Place the chopped rhubarb into a microwave safe bowl and microwave on high for 1.5 to 2 minutes.
The rhubarb should just be turning soft but still, have shape.
Drain any liquid from the rhubarb with a sieve.
Spoon the rhubarb onto the filling, evenly distributing it around the tart.
Bake for approximately 1 hour. The center should be set, and not runny and the edges should just have a hint of golden colour.
Remove the tart from the oven and let it cool on a wire rack for 1 hour before cutting.