Melt butter over medium heat in a 1 quart saucepan, and whisk in flour until well blended and smooth. Now very gradually stir in the milk. When milk is combined, add sugar, salt and pepper. Cook and stir until sauce beings to boil. Stir and boil 1 minute. Add frozen peas and stir.
Cover pan and allow to simmer for 5 minutes over medium heat. Do NOT over cook these! Soggy peas will ruin this dish. You want them tender but firm.