For the dressing: Whisk
together the mayonnaise, vinegar, mustard, garlic in a bowl and season with salt and pepper. Let sit while potatoes boil to allow the flavors to meld.
For the salad: Preheat the oven to 375 degrees F. Toss the poblanos with a few tablespoons of canola oil
and sprinkle with salt and pepper. Put the poblanos on a baking sheet and roast
until the skin is blackened
on all sides, turning a few times, about 25 minutes. Transfer to a bowl and immediately cover with plastic wrap
. Let sit and steam for at least 15 minutes and up to a few hours. Transfer to a cutting board and remove the skin and seeds. Thinly slice the poblanos and set aside.
While the chiles are roasting, put the potatoes in a large saucepan
and cover by 2inches of cold water. Add 2 tablespoons salt to the water and bring to a boil over
high heat. Cook until a skewer
or paring knife inserted into the center of the potatoes meets no resistance, about 25 minutes (depending on the size of the
and let cool for at least 5 minutes on a cutting board. Cut the potatoes into 1-inch dice
Heat 3 tablespoons canola oil in a large cast-iron skillet over high heat until the oil begins to shimmer. Add the potatoes in a single layer and cook, pressing firmly with a spatula
, until a crust
has formed on the bottom. Gently turn them and cook until all sides are golden brown and crisp
, adding more oil if needed. Transfer the potatoes to a bowl, add the chiles, radicchio and dressing
and stir gently to combine. Fold in the cilantro
and green onions
and serve warm or at room temperature.