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