Step 1

Position a baking rack in the center of the oven and preheat to 400 degrees. Lightly grease a large, rimmed baking sheet with oil.

Step 2

Make the potatoes: Place a potato lengthwise between two identical round handles of wooden spoons. Using a sharp knife, make slices every 1/8 inch across the width of the potato, using the handles as a guide to stop the blade from cutting all the way through. Leave about a 1/2-inch of uncut potato at each end. Repeat with the remaining potatoes.

Step 3

Place the potatoes, one at a time, in the microwave and cook on HIGH for 2 minutes. The potatoes will not be soft, but the slices will be easier to manage.

Step 4

While the potatoes are cooling, in a medium bowl, combine the softened butter, garlic, parsley, salt and pepper until well blended. Transfer about 4 teaspoons of the compound butter to a small bowl, then cover and set aside. In a separate small bowl, combine the Parmesan and panko, if using, then cover and set aside.

Step 5

When the potatoes are cool enough to handle, working with one potato at a time, spread the butter mixture between the slices. The slices will be stiff, so take your time, using your hands to tuck a little butter into each slice and a butter knife, if necessary, to push the butter down between the slices. Rub butter on the outside of the potatoes, as well.

Step 6

Place the potatoes on one end of the sheet pan, fitting them snugly together, and loosely tent with aluminum foil, tucking it under the potatoes. Transfer to the oven and roast for about 45 minutes.

Step 7

Make the chicken: While the potatoes are roasting, pat the chicken dry with paper towel. In a small bowl, combine the thyme, sage, salt and pepper.

Step 8

Drizzle about 2 tablespoons of the olive oil over the chicken, rub to coat, and gently rub some under the skin, making sure not to break the skin. Generously season the chicken with the seasoning blend, rubbing some under the skin and inside the cavity of the bird.

Step 9

Cut the lemon into 2 pieces and insert them into the bird, gently squeezing to release their juice. For a prettier presentation, tie or truss the legs together with kitchen twine, if you have some. Lightly cover with a clean towel or plastic wrap and set aside until ready to roast.

Step 10

After the potatoes have cooked for 45 minutes, remove the foil and uncover the chicken and add it to the center of the sheet pan, leaving the remaining third of the pan empty.

Step 11

Return the pan to the oven and roast the chicken and potatoes for about 15 minutes.

Step 12

Make the Brussels sprouts: While the chicken and potatoes are roasting, trim any tough outer leaves or stems from the Brussels sprouts and slice any large ones into halves or quarters, so all of the pieces are roughly the same size. (The smaller the pieces, the more caramelized they will become.) Transfer the Brussels sprouts to a medium bowl and add the olive oil, sugar, lemon juice and zest, salt, pepper and crushed red pepper flakes, if using. Using your hands or a large spoon, toss to coat evenly. Cover and leave on the counter.

Step 13

After 15 minutes, remove the pan from the oven. Using tongs, gently squeeze the base of each potato to open and fan the slices. Sprinkle the potatoes with the Parmesan cheese and panko mixture, if using, working it down into the slices.

Step 14

Spread the Brussels sprouts on the sheet pan, sliced side down, if halved, filling the empty third of the pan and placing them wherever they will fit around the chicken and potatoes.

Step 15

Return the sheet pan to the oven for an additional 45 minutes, or until the chicken is done, the potatoes are tender and the Brussels sprouts start to darken and caramelize.

Step 16

To check if the chicken is done, insert an instant-read thermometer in the thickest part of the chicken’s leg or breast, not touching the bone. It must register at least 155 degrees. Let the chicken rest for 10 minutes and test the temperature again, before carving. It should read 165 degrees.

Step 17

When ready to serve, run a fork along the top of the potatoes to further fan out the slices. Place a dollop of the remaining seasoned butter over each potato.

Step 18

Sprinkle fresh parsley over the chicken, if using.

Step 19

NOTES: To make gravy: After transferring the food to serving platters and while the pan is still warm, free up all of the bits stuck to the pan. (If the pan is a bit dry, add a few tablespoons of hot water or stock and use a spatula to scrape them off the pan.) Then, using a rubber spatula, scrape the bits and as much of the drippings as you can into a bowl. (For a 4 1/2-pound chicken, you should end up with about 1/2 cup of jus, depending on how juicy your bird is.)

Step 20

In a small pan, make a roux by melting 1 tablespoon of butter and then adding 1 tablespoon of all-purpose flour and cook over medium-high heat, stirring constantly, until it turns deep brown, about 3 minutes. Add the drippings and, if need be, a few tablespoons of hot water or chicken stock. Simmer for about 1 minute. Taste and season with salt and pepper, if needed. If the gravy is too thick, add more stock or water, 1 tablespoon at a time. (Makes about 1/2 to 3/4 cup gravy.)

Step 21

It will take a 4 1/2-pound chicken from 1 hour to 1 hour 15 minutes to cook if roasted at 400 degrees. If the chicken is smaller or larger, reduce or add about 10 minutes per pound, 5 minutes per half pound.

Step 22

If potatoes are larger than about 8 ounces each, they will need to cook longer. This will vary, depending on the size. If, after cooking as directed, they are not tender, leave them in the oven until tender when pierced with a fork, checking them every 10 minutes.