Preheat the roasting pan to give the vegetables a crisp, golden crust.
Heat oven to 425 degrees. Set a heavy roasting pan in the oven, and allow to preheat for 20 minutes.
Meanwhile, cut each fennel bulb lengthwise into six wedges. Season fennel and potatoes with salt and pepper, and toss with olive oil.
Remove roasting pan from oven, and place fennel and potatoes, cut side down, in hot pan. Return pan to oven, and roast vegetables for 30 minutes, without turning, until tender and golden brown. Serve immediately.