Place the potatoes in a large pot and cover with salted water. Bring to a boil and simmer for about 15 minutes or until tender. In a separate saucepan, boil the peas for 6-7 minutes.
In a medium saucepan, melt the butter over medium heat. Stir in the flour and cook for 1 minute. Gradually whisk in the milk until the mixture thickens to a creamy consistency.