In a heavy sauce pan melt butter and saute diced onions for 5--7 minutes on a medium heat until they are translucent. Stir in flour then add half and half. whisk for a minute or two until mixture is well incorporated. Bring to a gentile simmer. Season with old bay, pepper,salt,hot sauce and sherry. Add pepper jack cheese, stir until melted then add crab meat. Gently stir until crab is warm. Finish with parsley and green onion. Serve with crackers, tortilla chips or bagel chips.