Remove the tough base and the stalks from the fennel.
Set aside the green fronds.
Rinse and slice the bulbs.
Put in a dish with the white wine.
Cover and microwave on HIGH for 14 minutes.
Puree the fennel in a food processor, adding the mustard and salt and pepper to taste.
Puree until smooth.
Pour the puree into a deep dish.
Add the instant potato flakes and stir well.
Add the butter and stir again.
Sprinkle with the fennel fronds