Pre heat oven to 200c ff / 390f.
Place wedges of potato & fennel on to a baking tray with sides approx 3cm / 1 1/4" high. (See notes) Pour in water, then cover tightly with foil and bake for 40 mins.
Meanwhile to make the cream sauce, combine cream, garlic powder, mustard, 50g of grated parmesan and salt & pepper in a jug and mix to combine - then set aside.
To make the crumb, mix together the bread crumbs and remaining 10g of parmesan cheese and set aside.
Remove potatoes from oven, and carefully remove foil - steam will escape.
Spoon the cream mixture over the potatoes and fennel, in particular the high spots, then sprinkle over the crumb mixture.
Grill / broil for 7 - 10 mins (see notes) or until cream sauce is bubbling.