2 poblano chiles
3 pounds (about 4) Russet potatoes, peeled and cut into 1-inch cubes
1 tablespoon kosher salt
8 tablespoons unsalted butter
4 cloves garlic, minced
1 cup half and half
1/4 cup buttermilk
First, roast the poblanos under the broiler until blackened on both sides, about 10-12 minutes, turning once. Once blackened, place the chiles in a paper sack or plastic food-storage bag, close it tight, and let the chiles steam for 20 minutes. After the chiles have steamed, remove from the bag, and rub off the skin. Remove the stems and seeds from the chiles and finely dice.
Meanwhile, to make the mashed potatoes, place the potatoes in a large pot, cover with 1 inch of water, add about 1 tablespoon of kosher salt, and bring to a boil on medium heat. After the water comes to a boil, turn the heat to medium-low and continue to cook until the potatoes are fork-tender (be sure not to overcook), about 10-12 minutes. Drain and rinse, then lightly salt and pepper the potatoes.
Wipe out the pot, then add the butter and melt it over low heat. Add the garlic, and while stirring, cook until fragrant and softened about 30 seconds. Turn off the heat. Return the potatoes to the pot, and with a masher, mash the potatoes until smooth.
Pour in the half and half and buttermilk, and stir until well blended and creamy. (I leave off the heat to prevent the potatoes from burning on the bottom, but if you find they’re not hot enough, use low heat but keep stirring to prevent them from sticking.) Stir in the chiles, then taste and add more salt and pepper if desired.