Grainy Creole mustard adds texture and a delightful kick to the dressing, and roasting the lemons and oranges heightens both the sweet and sour flavors, creating a wonderfully nuanced balance. If you can find satsuma oranges, definitely use them to add a bright sunshiny tang. You can make the vinaigrette and pecans several days ahead.
1 lemon, halved, bottoms trimmed flat
1 medium-size orange or 2 satsuma oranges, halved
1 tablespoon sugar
1 tablespoon sherry vinegar
2 tablespoons Creole mustard
2 teaspoons honey
1 garlic clove, minced
Freshly ground black pepper
2/3 cup extra virgin olive oil
6 cups packed mixed bitter greens (such as frisée, radicchio, and arugula)
Preheat broiler with oven rack 3 to 5 inches from heat. Pat lemon and orange halves dry with a paper towel, and sprinkle cut sides with sugar. Place, cut side up, in an aluminum foil-lined jelly-roll pan, and broil 5 to 8 minutes or until caramelized and slightly softened. Cool in pan on a wire rack 10 minutes.
Squeeze juice from broiled citrus into a small bowl. Stir in vinegar and next 3 ingredients. Add salt and pepper to taste. Let citrus mixture stand 10 minutes. Add oil in a slow, steady stream, whisking constantly until smooth.
Toss together greens, onion slices, and apple slices with desired amount of vinaigrette in a large bowl. Refrigerate any remaining dressing to use later (up to 1 week). Season salad with salt and pepper, and toss again. Sprinkle with cheese and pecans.