01 - Place halved potatoes in a large saucepan and cover with cold, salted water. Bring to a boil over medium-high heat. Reduce heat and simmer for 12-15 minutes until fork-tender.
02 - Add peas to the pot with potatoes during the last 3 minutes of cooking. Drain and set aside.
03 - Melt butter in a large skillet or saucepan over medium heat. Whisk in flour and cook, stirring constantly, for 1-2 minutes to form a roux.
04 - Gradually whisk in milk followed by heavy cream, stirring until sauce is smooth and begins to thicken, about 3-5 minutes.
05 - Season sauce with salt, pepper, and nutmeg if using.
06 - Add drained potatoes and peas to sauce, gently folding to coat evenly. Cook for 2 minutes to heat through. Transfer to serving bowl and garnish with fresh parsley.