Melt butter in a 4 to 5-quart pan over medium heat.
Add onion and garlic and cook, stirring occasionally, until onion is soft.
Add curry powder and cook, stirring, for 2 minutes.
Add flour and cook, stirring, until bubbly.
Remove pan from heat and gradually stir in milk.
Return to heat and cook, stirring, until sauce boils and thickens.
Blend in pepper and sherry.
Add turkey and stir until heated through.
Season to taste with salt.
Serve curry over rice; pass condiments at the table to add to each serving.