Although I like the basic taste of radicchio a lot, I frequently get heads that are so bitter as to be basically inedible. Can you suggest some cooking techniques that are particularly effective at reducing the bitterness without masking the other flavors too much?
Braising gently in milk will also, I find, help with bitterness. The radicchio becomes wonderfully succulent, very nice with a firm-fleshed fish.
Roasting and grilling seem to help. You can also lessen the harshness by using ingredients with a sweet flavor profile in conjunction with it.
Years ago I tried a Radicchio appetizer (basically a radicchio bruschetta...but this was mid to late 80's and bruschetta wasn't something that was as common then!) I believe it came from Sunset Magazine or Better Homes & Gardens:
Dice up the radicchio and place into a baking dish. Infuse some olive oil with garlic and dry herbs of choice (I think it had thyme, pepper, and oregano). Drizzle the oil over the diced radicchio and roast until radicchio is tender. Then crumble goat cheese over the top and bake until cheese is softened. Serve the roasted radicchio and goat cheese piled onto crostini.
Soaking for a while in cold water beforehand also helps tame the bitterness.