FOR THE HOT HONEY: Combine chile slices with honey in a medium-size pot and bring to a boil. Remove from heat. When cool, strain honey into a jar. Finely chop chile slices and place in a jar with a lid that you will use for your salad dressing.
FOR THE GARLIC LEMON OIL: Pour olive oil into a jar. Stir in garlic and lemon zest.
FOR THE DRESSING: To the jar with the chopped chiles, add the vinegar, olive oil, fish sauce, crème fraîche, hot honey, and garlic. Shake vigorously until emulsified. Taste and adjust. You want it sweet and acidic enough to hold up to the bitter greens.
FOR THE GRILLING AND ASSEMBLY: Cut the Treviso radicchio in half lengthwise. Trim off any unappetizing bits of the stem but make sure to leave enough to keep the leaves connected at the base. Place halves cut-side up on a cookie sheet. Generously drizzle with the garlic lemon oil and season with the salt.
Heat a ridged or flat cast iron pan over high heat. When the pan is smoking hot, place radicchio halves cut-side down in the pan. Grill until slightly charred, about 30 seconds. Flip over and grill the other side for about 10 seconds.
Arrange radicchio halves on a platter, cut-side up. Drizzle with dressing, making sure it seeps down in between the leaves. Scatter with pistachios and ricotta salata wisps. Drizzle with hot honey.
MAKE AHEAD: This salad holds its shape and tastes even better the next day.