Preheat oven to 180C. Cut 4 fennel bulbs into wedges (reserve fronds) and set aside. Heat half the oil in a large frying pan over medium-high heat, add fennel wedges in batches and cook, turning once, until golden (1-2 minutes each side). Transfer to a roasting pan large enough to fit fennel wedges in a single layer and set aside.
Add onion and half the garlic to frying pan, stir occasionally over medium-high heat until tender (2-3 minutes), then scatter mixture over fennel. Deglaze pan with Pernod, add stock, half the lemon rind and half the lemon juice, season to taste and bring to the boil. Pour over fennel wedges, roast until tender (25-30 minutes). Remove fennel wedges and keep warm, then simmer braising juices over high heat until reduced to 40ml (4-5 minutes).
Meanwhile, thinly shave remaining fennel on a mandolin and place in iced acidulated water with reserved fennel fronds until crisp.
Dry-roast fennel seeds until fragrant (1 minute), coarsely crush in a mortar and pestle then transfer to a bowl. Add reduced braising liquid, remaining garlic, lemon rind and juice and remaining oil, season to taste and whisk to combine.
Arrange braised fennel on a platter, scatter with shaved fennel and fennel fronds, drizzle with fennel-seed dressing and serve warm.