First, score the duck skin almost, but not quite, through the fat. Score diagonally about 1cm (1/2") apart, then trun round and score the other way to form 1cm (1/2") diamonds.
Next, boil a kettle full of water, and pour it over the skin side, while the breasts are resting on some sort of grid.
Dry the duck breast very well, and, if you have time, allow them to dry out in the fridge for a few hours.
If you are adding flavour, use a dry rub on the skin side only (5 Spice goes well with Duck)
Next preheat the oven to 200C 400F.
Get an ovenproof frying pan that will fit in the oven, and put it on a medium heat on the hob.
Lay the duck breasts, skin side down in the dry pan - do not add oil or fat, and allow them to cook fairly slowly without moving them, check after 5 mins, by raising a corner - you want the skin crisp and looking a bit like crackling - it should be "golden brown. Don't rush this step, as you want to cook most of the fat out of the duck breast. There will be a great deal of fat!
When the skin side is brown and crispy, wi8th the diamonds slightly shrunken, turn the breast over, skin side up.
Give it about 3/5 minutes, then pour off and save the duck fat (use it for roasting potatoes, its delicious). Put the pan with the duck breast skin side up in the oven, and cook until done - 6 mins for rare, 8 mins for medium, 10 mins for well done - you can check with a meat thermometer.
Carefully remove the pan from the oven, using oven gloves. Be very careful - the handle will be hot. Allow the breast to rest for about 5 mins while you prepare the plates.
You can either slice the duck breast before you put it on the plate, or simply serve it whole.
This method will produce the crispiest skin, and the tenderest duck - give it a try.