For the chicken and potatoes:
2 1/2 pounds Yukon Gold potatoes, cut into 1 1/2-inch cubes
1 medium yellow onion, roughly chopped
2 tablespoons olive oil
1 4-pound whole chicken
1 medium lemon, quartered
Handful fresh sage
3 teaspoons salt, divided (I like a flaky sea salt here)
Preheat the oven to 475°F. Combine the potatoes and onion in a large oven-proof skillet and toss with the oil and 1 teaspoon of the salt. Spread evenly over the bottom of the skillet.
Remove the neck and any giblets from the cavity of the chicken, and then stuff the lemon and sage inside. (Optional: Flip the wings under the back of the chicken, and cross and tie the legs together.) Sprinkle the chicken all over with the remaining 2 teaspoons salt, paying special attention to the area over the breasts, thighs, and drumsticks.
Place the chicken on top of the potatoes in the skillet, breast-side up. Transfer the skillet to the oven and roast the chicken for 50 minutes. After 50 minutes, check the temperature in the thickest part of the thigh. The chicken is done when it registers 165°F; continue roasting if needed.
Remove the chicken from the oven and transfer to a cutting board. Let it rest for 10 minutes, then carve. Serve warm with the potatoes.