Boil potatoes in salted water until just done/fork tender, approximately 10-15 minutes depending on the size of your potato cubes (you don't want them overdone or they will get mushy real quick). Drain and set aside.
In a medium-sized saucepan, melt butter over medium heat.
Slowly add flour, stirring, until flour/butter mixture becomes doughy (you may not need all the flour).
SLOWLY add milk, whisking constantly until mixture becomes smooth and creamy. You want it to be a gravy consistency so add more milk if it seems too thick. Add salt and pepper, to taste.
Add peas and bring to a slight simmer.
Carefully stir potatoes into creamy mixture until potatoes become well covered and serve!