Start with a mild, flaky white fish—we went with Atlantic cod, but halibut, black cod, or even skate wing can also be substituted here. Just be sure to reduce the cooking time accordingly for thinner fillets. To prevent sticking, use a large, heavy-duty skillet and a mixture of olive oil and butter to sear the cod. I like this textured stainless-steel pan: the light color makes it easy to see when the butter has fully browned, and the textured interior keeps the delicate fillets from adhering and tearing. A good-quality, unscratched nonstick skillet or even a lighter-weight cast-iron one will also get the job done, but be prepared to rely on your nose when toasting butter in a dark-colored pan.