Terrific Green Salads
In a large skillet, heat the olive oil until shimmering. Add the chopped fennel bulbs and cook over moderately high heat, stirring frequently, until golden and tender, 8 to 10 minutes. Let the chopped fennel cool in the skillet for 10 minutes, then stir in the vinegar and lemon juice and season with salt and pepper. Reheat and stir in the fennel fronds just before serving.
The vinaigrette can be refrigerated overnight.