For the roast fennel:
For the potato salad:
First, roast the fennel. Preheat the oven to 180C. Cut each fennel bulb in half lengthways, then cut again lengthways into wedges about 2cm thick. Toss with around 2 tablespoons of olive oil and some seasoning, then spread on a baking tray and roast for 30 minutes, turning occasionally, until tender to the point of a knife and caramelised.
Meanwhile, boil the potatoes in salted water for 15 minutes or until tender. Drain and leave to cool. Whisk together the oil, lemon juice, crème fraiche, salt and pepper, then toss with the radishes, mint leaves, chives and lemon thyme or lemon verbena leaves (if using lemon verbena, finely slice the leaves). When the potatoes are cool enough to handle, chop into bite-sized pieces and toss with the salad. Serve with the roast fennel and trout fillets, with lemon wedges on the side.