Heat milk in a small saucepan over medium heat until it begins to boil. Stir milk powder and sugar into the hot milk until dissolved. Remove from heat and let cool until an instant-read thermometer reads 43 C.
Place yogurt in a bowl and add a small amount of warmed milk mixture; combine thoroughly. Pour yoghurt mixture back into the saucepan with warmed milk in a thin stream, stirring constantly, until thoroughly blended. Add cream and flavouring; stir well to combine.
Pour milk-cream mixture into 7 individual serving jars. Process in a yoghurt maker, according to manufacturer's instructions, for 8 hours. Chill at least 3 hours before serving.