1.Lightly grease a 13 x 21cm loaf pan. Line pan completely with plastic wrap, extending 5cm above sides of pan.
2.Melt butter in a large frying pan on medium. Saute leeks and mushrooms for 4-5 minutes until tender. Cool.
3.Arrange 4 slices of prosciutto widthways in pan, covering base and sides and allowing it to overhang. Spread half leek mixture over prosciutto. Top with half the basil leaves, then half the capsicum. Cover with 2 slices prosciutto, trimming to fit pan.
4.Repeat layers, finishing with prosciutto. Fold overhanging prosciutto over this, pressing down firmly. Wrap plastic wrap tightly over to enclose terrine. Place heavy cans on top of terrine and chill for 8 hours or overnight.
5.When ready to serve, remove from pan and unwrap. Slice terrine and serve with cornichons, pickled onions, olives and crusty bread.
If preferred, char-grill your own capsicum by roasting until skin chars. Simply remove skin, seeds and membrane, and then use as directed.Note