Pre-heat oven to 450 degrees F.

Fill a large pot with cold water and cut potatoes.

Cook on high until potatoes are fork-tender but not falling apart.

When ready drain the potatoes and set them aside.

On a cutting board finely mince rosemary leaves, garlic cloves, kosher salt, and red pepper flakes. Mince together until paste forms.

Add herb paste to a medium-sized bowl and mix with the juice of 1 lemon and olive oil.

Add chicken and coat thoroughly.

Heat a large 12-inch cast-iron skillet over medium-high heat.

Add the chicken thighs, skin-side down, and cook until the skin is brown and crispy.

Remove from the pan, add the mushrooms and potatoes, and drizzle with any remaining chicken marinade and juice from the remaining lemon.

Top with chicken, skin side up.

Add rosemary sprigs and squeezed lemon halves to skillet and roast, uncovered, until skin is crisp and chicken is cooked all the way through, about 25 minutes.