In a large sauce pan over medium heat, melt butter. Saute 1 sm onion chopped for a few minutes until onions are translucent, add 3 garlic cloves finely chopped and saute for another minute being careful not to burn garlic. Add 1/2 c. fresh corn and mix well together with onions and garlic. Saute corn for about 5-10 minutes until corn is cooked and starchiness of corn is gone. Add 1 12 oz Mexican beer and get it really hot. In the meantime rinse clams well and discard any clams that do not close. Add clams to pan and cook until shells open. Add parsley and zest to clams and stir. Serve clams in individual bowls and garnish with more parsley and lemon or lime wedge.