Add bacon grease to a large pot. When melted, whisk in flour. Continue whisking until the flour disappears. Slowly pour in half and half while constantly whisking. Bring to a low boil.
Add potatoes and English peas, butter, salt and pepper. Stir.
Cover and cook over medium low heat until potatoes are tender. Stir often.
Before serving, check for seasoning and adjust.
Serve warm.