Preheat oven to 200°C/400°F. Liberally season the chicken thighs with kosher salt and pepper.
Heat a large oven-proof skillet over medium high heat. When hot add the olive oil. Place the chicken thighs, skin side down, in the skillet. Sear the thighs until the skin is golden brown and crispy, about 5 to 7 mintues.
While the chicken is searing prepare the swiss chard. Cut the leaves off the stems and chop the stems into small pieces. Slice the leaves into large ribbons. Grate the zest off the lemons.
When the skin is browned flip the thighs and sear on the bottom for 2 to 3 minutes then remove to a plate and set aside. Check the level of fat in the pan, you may need to remove excess or add more to have 2 tbsp left in the pan.
Add the swiss chard stems to the skillet and sauté until just starting to soften about 2 to 3 minutes. Add the minced garlic and cook for another minute then add all of the chard leaves and the lemon zest. Sauté until the leaves are wilted.
Add the juice of 1 lemon and deglaze with the white wine. Let the wine cook until reduced by about half then add the chicken broth and 1 cup of the heavy cream. Bring to a simmer and then return the chicken thighs to the skillet, nestling them on top of the chard.
Transfer the skillet to the preheated oven and bake for 35 to 40 minutes or until the chicken thighs are cooked through to an internal temperature of at least 74°C/165°F.
To finish the sauce, remove the chicken thighs to a serving platter and remove the chard with a slotted spoon to a serving bowl. Add the remaining ¼ cup heavy cream to the sauce. Bring the sauce to a boil and let simmer until reduced by half and slightly thickened, about 3-5 minutes. Add the juice of the remaining lemon. Taste the sauce and adjust the seasoning if needed by adding more kosher salt or pepper and it's ready to serve!