1.Use a small sharp knife to cut the top and bottom from grapefruit and oranges. Cut off the rind with the white pith, following the curve of the fruit. Hold grapefruit over a bowl to catch the juices, then cut down both sides of the white membrane to release each segment. Reserve juice; you need 1 tablespoon. Cut oranges into slices.
2.Arrange grapefruit, orange, sliced fennel and witlof on a serving plate. Scatter with hazelnuts, herbs and chilli.
3.Whisk oil, vinegar and fennel seeds into reserved juice; season to taste.
4.Serve salad drizzled with dressing and topped with reserved fennel fronds.
Use a mandoline or V-slicer to cut the fennel into wafer thin slices. Use a mixture of oranges and blood oranges when they are in season.Note