1. Boil the sweet potatoes in a large pot of salted water until tender, about 15-20 minutes. Drain and set aside.
2. In a large saucepan over medium heat, melt the butter. Stir in the flour and cook for 1-2 minutes until the mixture is smooth and bubbly.
3. Gradually whisk in the milk and evaporated milk, stirring constantly until the sauce thickens and begins to simmer.
4. Season the sauce with pepper and salt, adjusting to taste.
5. Add the cooked sweet potatoes and peas to the sauce, gently folding them in until well coated and heated through.
6. Serve warm as a side dish or enjoy it as a comforting main course.