Place all ingredients except the vanillas into the Thermomix bowl and cook 8 min/80°C/speed 4.
Add vanilla bean paste and powder through the hole in the lid and blend 10 sec/speed 6.
Pour into a jug or bowl that doesn't retain the heat and cover with a cartouche. Allow to come to room temperature for a minimum of 2 hours.
Place into the fridge overnight or until completely cold.
Churn following manufacturers instructions.
Thermomix method; After cooling the custard completely, pour into a flat tray or ice cube tray and freeze overnight. Remove when frozen and return to the Thermomix bowl and blend until fluffy. You could insert the Butterfly once the entire mix is together and whip for a little just to aerate.