Trim and wash the fennel.
Cut into quarters and cook in boiling salted water with the lemon juice until tender - about 30 minutes.
Drain the fennel and slice roughly.
Melt the butter in a large saucepan and saute the fennel for a few minutes.
Stir in the flour, then add half the stock and milk, the ground mace and seasoning.
Finely chop the parsley, using the double-bladed chopping knife.
Place the fennel and stock mixture in the bowl with the parsley and puree until smooth, using the double-bladed chopping knife.
Return this mixture to the saucepan, add the remaining stock and milk and bring to the boil.
Simmer gently, stirring occasionally for 10-15 minutes.