Simmer 150ml double cream with lemongrass for one hour, purée, sieve, and chill.
Whisk egg yolks and 75g sugar over a double boiler until pale and fluffy.
Cook the egg mixture for 6 minutes while whisking until thickened.
Whisk the cold lemongrass cream into the egg mixture and chill until cold.
Whisk egg whites with remaining sugar to create a glossy meringue.
Fold the meringue gently into the lemongrass base.
Whisk 300ml double cream to stiff peaks and fold into the mixture.
Pour mixture into rings on a lined tray and freeze for two hours.
Boil sugar, honey, glucose, and water to 160°C then whisk in bicarbonate of soda.
Set the honeycomb on a lined tray and break into small pieces when hard.
Fry bananas until caramelised, remove, then cook butter and brown sugar to a caramel.
Add lemongrass and 150ml cream to the caramel, simmer, and warm the bananas through.
Coat the top and bottom of each frozen parfait with honeycomb pieces.
Unmould parfaits onto plates and serve with bananas and toffee sauce.