It's worth the time to blanch and peel pearl onions for this salad. We don't recommend using frozen pearl onions.
Trim bottom ends of onions. Blanch unpeeled onions, in batches, in rapidly boiling water in a large saucepan 45 seconds. (It's important to blanch in batches so that the water remains at a boil.) Drain and peel onions; place in a large zip-top freezer bag, seal, and refrigerate overnight, if desired.
Combine cabbage and 2 tablespoons salt in a large bowl; let stand 30 minutes, tossing occasionally. Rinse thoroughly, and drain well.
Combine onions and oil in a shallow roasting pan or a large cast-iron skillet; toss to coat. Spread onions in a single layer. Roast at 450° for 25 minutes or until browned, stirring after 20 minutes.
Combine 1/4 cup each vinegar and maple syrup; add to roasted onions. Roast 5 more minutes or until slightly thickened and onions are glazed. Set aside.
Combine remaining 2 tablespoons vinegar, 2 tablespoons maple syrup, 1 cup chopped pecans, sour cream, and 1/2 teaspoon salt in a food processor or blender; process 1 to 2 minutes or until smooth. Cover and chill dressing overnight, if desired.
Toss together chopped apple, cabbage, and endive in a large bowl. Drizzle each serving with dressing, and top with roasted onions; sprinkle with remaining 1 cup pecans.
Make Ahead: Blanch and peel pearl onions a day ahead; store in refrigerator. Prepare dressing up to a day ahead, and store in refrigerator.
Christmas with Southern Living 2005