How to Make It
Preheat the oven to 425°. In a pie plate, toast the walnuts for about 5 minutes, until golden and coarsely chop
Line 2 baking sheets with parchment paper. On one baking sheet, toss the fennel with 1 tablespoon of the olive oil; season with salt and pepper. Place the potatoes on the second baking sheet and toss with 1 tablespoon of the olive oil; season with salt and pepper. Turn the potatoes cut side down. Roast the fennel and potatoes for about 30 minutes, rotating the pans halfway through, until the vegetables are golden and tender.
Meanwhile, in a mini food processor, pulse the anchovies with the capers, garlic, lemon zest and lemon juice until finely chopped. With the machine on, drizzle in the cooled butter and the remaining 1/2 cup of olive oil and puree until smooth. Season the dressing with salt and pepper.
In a large bowl, combine the fennel and potatoes with the radicchio, endives and three-fourths of the dressing; season with salt and pepper. Transfer the salad to a platter and garnish with the walnuts. Serve the remaining dressing on the side.