Gather the ingredients.

Using a sharp kitchen knife, cut 5 to 6 even slashes across the skin of the duck breast, taking great care to not cut into the meat. Cutting the skin this way prevents it from shrinking and distorting the meat while cooking and also helps to release fat from underneath the skin.

Season with a generous pinch of salt and pepper.

Heat a ridged griddle pan or heavy skillet over medium-high heat. You want it hot, but not smoking. Lay the duck breast skin-side down; the skin should sizzle as it hits the hot pan. You do not need any oil since the fat under the skin will quickly begin to melt. Cook for 4 minutes.

Season the meat with salt and pepper before turning using tongs or a spatula. Cook the meat for 4 minutes.

Drain any fat into a bowl. Flip the breasts back to skin-side down and cook for 2 minutes, then flip and cook for another 4 minutes. This creates a very crisp skin and gently cooks the meat through to medium-rare. The duck should read 140 F on a thermometer. If you do not have a meat thermometer , the duck should be slightly firm when pressed.

Once the duck has reached the correct temperature, remove from the pan and drain any further fat into the bowl as before. Place the breasts in a dish and cover with aluminum foil. Leave in a warm but not hot place to rest.

Strain the duck fat through a fine sieve and reserve for another use.

To make the sauce (if using), place the pan back over high heat. Once hot, add the wine. Stir with a wooden spoon continuously while scraping up any residue from the bottom of the pan. Add the veal or chicken stock to the hot pan and boil until reduced by a third.

Strain through a fine sieve into a small saucepan. Boil and whisk in the cold butter a little at a time. Taste and adjust the seasoning. Add the blackberries to warm through just before serving.

Serve. If the duck has cooled too much during resting, reheat in the pan by placing the duck skin-side down again for 2 to 3 minutes or pop it into a warm oven for 5 minutes.