A walnut is a hard-shelled nut that grows on walnut trees, prized for its rich, slightly bitter flavor and brain-like appearance. When you crack open the thick, wrinkled shell (which takes some serious effort), you find the edible kernel inside, divided into two halves that look surprisingly like a tiny human brain, complete with folds and wrinkles.

Walnut trees can live for hundreds of years and grow quite large. The wood from these trees is valuable too: dark, strong, and beautiful, it's used for making fine furniture and musical instruments. If you've ever admired a fancy wooden desk or cabinet with rich brown coloring and interesting grain patterns, there's a good chance it might have been made from walnut wood.

People have eaten walnuts for thousands of years. They're nutritious and store well through winter, which made them important food before refrigeration existed. Today, you'll find walnuts in brownies, salads, banana bread, and many other foods. California grows a large share of the world's walnuts, with vast orchards producing billions of nuts each year. The distinctive walnut flavor adds depth to both sweet and savory dishes, and many bakers consider them essential for certain recipes.