Lightly rub the potatoes with olive oil and wrap each potato in tin foil. Pierce through the foil and skin of the potato with a fork a couple of times.
Bake the potatoes for an hour or until tender.
Toward the end of baking time, make the sauce by melting the butter in a large, 12-inch nonstick skillet over medium heat. Add the carrots, celery, onion, garlic, salt and pepper and cook, stirring often, until the vegetables are crisp-tender (but not mushy), about 5-7 minutes.
Sprinkle the flour over the vegetable mixture and cook, stirring constantly, for 1-2 minutes. The mixture will be crumbly.
Slowly add 1/2 cup of the chicken broth whisking quickly until thick and combined (adding a little liquid at a time will help avoid lumps). Continue adding 1/2 cup of the broth and milk at a time until it has all been stirred into the skillet and the sauce is smooth and creamy.
Cook the mixture at a low simmer for 5-7 minutes, stirring often, until the vegetables are tender and the sauce is thickened.
Stir in the peas and chicken and heat through. Season with salt and pepper to taste.
Serve over baked potatoes with cheddar cheese and cooked bacon, if desired.
Plan Ahead: this recipe calls for already cooked chicken so plan ahead. If you are working with uncooked chicken, here's a simple way to cook it up quickly (or you could try cooking it with the vegetables in the first step).Potatoes: I used to think it unnecessary to wrap the potatoes in foil and/or rub lightly with olive oil and just bake them unwrapped on the oven rack. But we hated how thick and inedible the skins became after baking - if you want soft, tender potato skins, a very, very light rub with olive oil covered in foil and you're good to go. It's worth the extra step.Sauce: if you like things extra saucy (or your baking potatoes are humongous) you might consider 1 1/2-ing or doubling the sauce.