Place the tomatillos and jalapenos on the grill and cook until the skins char and blister, 10 to 12 minutes. Remove the tomatillos and jalapenos from the grill and let cool.
Coat a large, wide straight-sided saute pan with olive oil and bring to medium-high heat.
Sprinkle the chicken generously with salt. Add the chicken legs and thighs, skin-side down, to the hot pan. Brown the chicken well on all sides. Remove from the pan and reserve.
Ditch the excess fat from the pan and add a few drops of new oil. Add the onions, season with salt and cook until the onions are very soft and aromatic, 7 to 8 minutes.
While the onions are cooking, coarsely chop the tomatillos and reserve. Chop the jalapenos into 1/4-inch dice and reserve with the tomatillos. If you want to tone down the heat, remove the seeds from the jalapenos before chopping.
Add the garlic to the pan with the onions and cook for 1 to 2 minutes.
Add the reserved tomatillos and jalapenos. Stir to combine and add the chicken stock, lime juice and zest. Taste and season with salt if needed (it probably will).
Return the chicken to the pan and bring to a boil. Reduce to a simmer and cover. Cook for 15 minutes.
Remove the lid and let cook for 15 more minutes. This will allow the stock to reduce. Taste for seasoning and adjust if needed.
For the sour cream: Combine the sour cream with the lime zest and juice and reserve.
Remove the chicken from the pan and stir in the cilantro.
Spoon the sauce over the chicken, sprinkle with cilantro leaves and serve with the lime sour cream.