Veggies: check. Pan: check. Preheat the pan: check. Now for the good part: Add the fat. The only question is: which type? Fat is a confusing and slightly loaded topic. Though our culture's fat pendulum is currently mid-swing somewhere between the fat-free '80s and '90s and the fat-only, carb-free '00s, I think it's safe to say that most people agree that fat + veggies = yum. Whether it's the olive oil in your salad dressing, or the butter on your sweet corn, fats have a way of complimenting and greatly enhancing the flavor of the foods we cook.
There are two basic lenses through which to view fats: the chef's lens and the nutritionist's lens. Here's a quick overview of what you'll see looking through each:
Chef's: Unless you're cooking a dish with a clear theme, like a Mediterranean dish where you would use olive oil, or an Asian dish where you may use sesame oil, butter is the big taste winner. Chef's tend to agree that butter browns meat and veggies beautifully and brings out tremendous flavor. However, butter also smokes at a lower temperature than oil, which isn't always great when sautèing, which needs to be done over high heat. Chefs also agree that once you should not let your fat (butter or oil) smoke in the pan! The ideal time to add your meat or veggies to the pan is before it smokes. The smoking degrades the quality and the flavor of the fat, and if it burns before you add your veggies or meats, it should be discarded as it will taint the entire dish. Because of this smoking issue, many chef's will recommend olive oil instead of butter, since it has an excellent flavor and is considered to be "heart healthy."
Nutritionist's: Speaking of heart healthy, many nutritionists and the USDA's dietary guidelines recommend limited intake of saturated fats, which are fats that are generally associated with animal meat and products like butter and cheese. Therefore, the conventional wisdom is that olive oil would be the natural choice for a healthy eater. However, it's important (especially as Vermonters who have access to some of the best artisanal cheese in the world!) to acknowledge that there are challenges to the anti-saturated fat mantra, and increasingly, articles and reports published suggest that eliminating saturated fat entirely is not beneficial to health.
Everyday Chef suggestion: Using olive oil is a safe bet, for your meal and for your health. Every now and then, when you're concentration is good (to watch carefully to prevent smoking) or when you're trying to impress, use butter. Also, keep an eye on the saturated fat debate; science is really keeping us on our toes.