Position a rack in the center of the oven and heat the oven to 350°F.
Put the pecans on a small rimmed baking sheet and toast until fragrant and pale golden on the cut sides, 6 to 8 minutes. Add the butter and 1/2 tsp. salt and toss with two heatproof spatulas until the butter is melted and absorbed by the nuts. Set the nuts aside (they can be added to the salad warm or at room temperature).
In a small bowl whisk together the vinegar, sugar, and 1/4 tsp. each salt and pepper. Slowly whisk in the oils until well combined.
Combine the radicchio, frisée, and pear in a large salad bowl and toss with just enough vinaigrette to coat. Add the nuts, toss, and serve.
nutrition information (per serving):
Photo: Scott Phillips