Trim off fennel stalks, reserving fronds. Trim bottom and tough outer layers from bulbs. Cut each bulb lengthwise into 8 wedges. Finely chop 2 tablespoons of fronds and set aside.
In a Dutch oven or deep saute pan, heat oil over medium-low heat. Add leeks and shallots and cook, stirring, until softened but not browned, about 4 minutes. Add wine, increase heat to medium and simmer for 2 minutes. Add fennel wedges and broth (or water) and season with salt. Bring to a simmer. Reduce heat to low, cover and simmer until fennel is tender, 15 to 25 minutes. With a slotted spoon, transfer vegetables to a bowl.
Whisk mustard into cooking liquid. Add spinach and lima beans, cover and cook until tender, about 5 minutes.
Return reserved vegetables to cooking liquid and cook until heated through, about 1 minute. Remove from heat and stir in sour cream and fennel fronds. Adjust seasoning with salt and pepper. Serve immediately.
Serves 4.