• Preheat the oven to 450°F, and adjust a rack to the center.

Roast the Vegetables

• Coat a deep 12-inch pie dish or 9 x 13 x 2-inch casserole dish with the olive oil. Add the potatoes, carrots, onion, sage and thyme to the dish and sprinkle generously with salt and pepper. Toss to be sure everything is well coated. Place the pan in the 450°F oven, and roast the vegetables until they're tender and golden, about 35 minutes. They should be mixed about halfway through. Set aside and reduce the oven to 375°F.

Sauté the Chicken

• While the vegetables are roasting, place the chicken breasts between two pieces of plastic wrap and gently pound them with a meat pounder (or the bottom of your smallest sauté pan). Their thickness should be even throughout so they cook evenly. Sprinkle both sides with salt and pepper.
• Coat the bottom of a large skillet with the olive oil and place it over medium-high heat. Once it's very hot, add the chicken breasts and sauté just until they're cooked through, about 7 minutes. Flip them over, and turn the heat to low-medium about halfway through. Set them aside to cool for at least 10 minutes. Then cut them into bite-sized pieces. Set aside.

Make the Sauce

• Add about ¼ cup of the stock to a small dish and add the cornstarch. Quickly whisk it until it's smooth. This is called slurry, and it will thicken the sauce. Set aside.
• Add the remaining chicken stock, the slurry, the buttermilk, cardamom, cinnamon and nutmeg to a medium-sized sauce pan and place it over low-medium heat. Cook, constantly whisking, only until it's very gently simmering, and then turn off the heat. Do NOT let it boil. (This whole process should only take a few minutes.)


Assemble

• Add the chopped chicken, peas and the sauce to the dish with the roasted vegetables and gently mix. Sprinkle with bread crumbs if desired for a bit of a crunch, and place it in the 3750°F oven for about 10 minutes, just to meld everything together.
• Serve!