Heat 4 tablespoons butter in a skillet over medium heat. Add next 5 ingredients and sauté until soft.
In a saucepan, heat remaining 2 tablespoons butter and stir in flour. Add milk and cook, stirring until thickened and smooth. Stir in salt, pepper and hot pepper sauce. Add sautéed vegetables and half-and-half.
Bring to a boil, stirring; reduce heat. Add crabmeat, simmer uncovered for 5 minutes. If desired, stir in sherry just prior to serving. Top with additional green onion.