In a large soup pot, melt butter over medium heat and add onions. Sauté onions until transparent. Add garlic and sauté for about 3 minutes more. Reduce heat to medium-low. Add flour a little at a time, stirring constantly. A blonde roux will form. Add seasonings and continue stirring. Gradually add half & half and milk, while stirring constantly. Raise heat to medium-high, bring just to a boil, then reduce heat to medium-low. Add both cans of corn and crabmeat and partially cover. Simmer for about 15 minutes. Taste soup and season to your preference. Serves 8 as an appetizer.