Cut off fennel stalks and remove strings from the bulbs with a vegetable peeler. Cut each bulb into 8 wedges, but do not remove the core. Bring salted water to a boil in a large saucepan, add fennel and blanch for 5 minutes. Remove with a slotted spoon, blot with paper towels and set aside.
In a large cast-iron or non-stick skillet, heat 1/2 T butter and 1/2 T oil together over medium high heat. Add half the fennel and saute until nicely browned on all sides, about 8 minutes. Transfer to a dish and reserve. Repeat with the remaining butter, oil and fennel. Add onions to the skillet,
sprinkle with sugar and saute shaking the skillet back and forth, until nicely browned, 5 to 6 minutes. Return the fennel to the skillet; add carrots and 1 c stock. Season with salt & pepper and simmer, covered, until the vegetables are tender 15 to 20 minutes, adding more stock as necessary to keep the stew moist. Garnish the fennel fronds or parsley.