Cotija is an aged, crumbly, slightly salty Mexican cheese traditionally made from cow's milk. The texture is somewhat akin to feta, and the cheese is excellent in pasta and salads, or as a garnish for tacos, quesadillas, and refried beans. Or serve Mexican-style corn on the cob by brushing grilled ears of corn with mayonnaise, then rolling them in crumbled cotija cheese and sprinkling with chile powder. Look for cotija in Latin American grocery stores.
Feta cheese is the best substitute.