It looks like a small-ish head of lettuce, the broad leaves on the outside that have jagged edges. It’s a variety of endive, which is evident by its bitter taste, and also the more tender, paler leaves in the core of the lettuce head. The outer leaves are a more vibrant, dark green color. During the season, spring through summer, escarole can be found at farmers markets. You can find it year-round in supermarkets and grocery stores near the endive, chicory, radicchio, and other greens. Look for firm heads with unblemished leaves. Any leaves that are tinged with brown will be particularly bitter, so remove them before using the escarole. Young pale leaves can be used in Escarole Salad.