For slicing or chopping large quantities, use a food processor with the slicing or wing blade attachment. If a recipe calls for just caps, twist stems loose or separate them from the caps with the tip of a knife. For each 8 ounces of mushrooms, melt 1 tablespoon of butter or heat 1 tablespoon of oil in a large skillet. Cook and stir until golden and the released juices have evaporated, about five minutes. Don't overcrowd the skillet or the mushrooms will steam rather than brown.
Mushrooms cook extremely well in the microwave.
Place mushrooms in a shallow baking pan, toss with a little oil and roast in a 450 degree oven, stirring occasionally until brown, about 20 minutes. Use about one tablespoon of oil for each 8 ounces of mushrooms. Lightly brush caps and stems with oil to keep them moist, and season with salt and pepper. Grill or broil 4 to 6 inches from heat source for 4 to 6 minutes on each side, brushing again once or twice. They're best when used within several days after purchase.