Add flour and stir with a whisk for 1 minute, taking care not to brown the flour and butter mixture. Continue stirring constantly and gradually add the milk, salt, pepper, and sugar. Heat to a simmer and continue cooking, stirring constantly, for one minute.
Add peas and heat to a simmer. Reduce heat and cover, simmering for 3-5 minutes. Peas should be tender-crisp, so take care not to overcook.