In a 2-quart saucepan, melt butter over medium-high heat. Stir in flour, salt, white pepper; cook and stir for 2 minutes. Mix in bouillon granules, onion, and half of the half-and-half. Bring mixture to a boil.
Reduce heat to medium; add shrimp and crab meat. Cook, stirring occasionally, until mixture thickens and shrimp are cooked through. Stir in remaining half and half and wine. Serve hot.