Step #1 Melt the butter in a thick bottomed saucepan, add the onion & celery & cook carefully for about 5 mins until transparent.
Step #2 Stir in the flour, mixing it in carefully to ensure that no lumps of flour are left; continue cooking carefully for another 5 mins, taking care that the vegetables don’t brown.
Step #3 Remove from heat & add the kumara, then slowly add the stock' stirring to mix all ingredients.
Step #4 Return pan to the heat & bring soup to the boil, add the bouquet garni then simmer for 45–50 mins, stirring every once in awhile.
Step #5 Take the pan off the heat, remove the bouquet garni & any foam that has formed.
Step #6 Allow to cool slightly then liquidize soup in a mixer.
Step #7 Add seasoning to taste then re-heat if necessary before serving.