In a large skillet, melt 2 tablespoons of the butter over medium-high heat. Add the eggplant, onions, salt, and cayenne and cook, stirring, until the vegetables are soft, 6 to 8 minutes.
Add the remaining 4 tablespoons butter and the flour and cook, stirring, for 3 minutes. Stream in the milk, stirring constantly, and cook until the mixture thickens, about 4 minutes.
Reduce the heat to medium and add the shrimp. Simmer for 4 minutes. Remove from the heat. Add the crabmeat, oysters, cheese, and green onions and stir gently to mix. Serve hot.
Yield: about 8 servings