We like a method we believe we picked up from Great Good Food (Canada, UK). You place chicken breasts on a microwave-safe plate (in a pinwheel or spoke pattern with the thickest part of the breasts toward the edge of the plate), pour a half-cup or so of buttermilk over the breasts, sprinkle them with a bit of thyme, cover the plate tightly with plastic wrap, and microwave on high for several minutes.
How long the breasts cook depends on how many you’re cooking, how thick they are, and how much oomph your microwave has (a note in the book recommends 8 minutes for two breasts, but we check it early). The microwave method can result in overheating the thinner portions of the breasts, so keep a close watch. The buttermilk will separate and the solids will curdle, but that doesn’t matter. Throw out the separated buttermilk mess, rinse off the chicken, let it cool, and shred away. It is delicious.
A non-microwave option is to poach the breasts in water, chicken stock, and/or wine. Arrange the breasts in a single layer in a heavy skillet or flameproof casserole, season with salt and pepper, add the liquid almost to cover, and add a bay leaf, some parsley and thyme. Cover and simmer on top of the stove or in the oven at 325°F (160°C) for about 10 minutes.
With either method, you have to cook the chicken enough so that it will shred easily, but the last thing you want to do is overcook it.