In a large ovenproof pan (2.5 L), combine water, erythritol, oranges, vanilla beans/seeds, and place on medium heat, stirring until erythritol has dissolved. Cook on medium to low heat for 10 to 15 minutes. Remove from heat.
Place almonds into Thermomix bowl and mill for 10 sec/speed 7.
Add remaining ingredients into Thermomix bowl. Mix for 30-40 sec/speed 7, or until well combined.
Spread batter over the oranges, spreading the mixture to the edges of the pan.
Bake for 30 to 40 minutes, (cooking time depends on the pan size).
After 5-10 minutes, turn upside down onto a a large plate.
Allow to cool and serve with warm coconut custard.
Place cornflour and sugar into Thermomix bowl, mill 10 sec/speed 10.
Add milk and cook 100 C, 7 to 8 min/ speed 4.