Cut the cleaned leeks into two-inch pieces, then place in a large skillet.

Cover and cook in a small amount of boiling water for 30 minutes or until tender.

Drain, then rinse with cold water; then drain again.

Transfer the leeks to a serving dish; then set aside, keeping warm.

Melt 2 tablespoons of butter in a heavy saucepan over low heat. Add the flour, stirring until smooth, then cook for 1 minute, stirring constantly, until sauce is thickened and bubbly.

Stir in remaining the butter, and salt and pepper.

Pour the sauce over prepared leeks and serve immediately.