Spinach Salad with Grilled Onion and Tahini Vinagairette

The first time I made this, I thought it was life-changing, but the second time the dressing didn't turn out quite right. I need to make it again and get some more perspective on it. --Lauren

Vinaigrette
1/2 cup water
1/4 cup white wine vinegar
3 tablespoons tahini (sesame seedpaste)
2 tablespoons coarse-grained mustard
1 teaspoon honey
1 small garlic clove, minced
3/4 vegetable oil

Salad
2 large red onions

12 cups (packed) baby spinach,trimmed
10 large radicchio leaves

For Vinaigrette:
Combine all ingredients except oil in blender and blend well.
Gradually blend in oil. Season to taste with salt and pepper.

For Salad:
Cut onions lengthwise into 1/2-inch-thick wedges, leaving root ends
intact. Place onions in 15x10-inch glass baking dish. Pour 1 cup
vinaigrette over onions, coating evenly. Let marinate 3 hours.
Chill remaining dressing. (Can be made 1 day ahead. Chill onions.)

Prepare barbecue (medium-high-heat) or preheat broiler. Sprinkle
onions with salt and pepper. Grill or broil onions until golden.
turning occasionally, about 12 minutes. (Can be made 6 hours ahead. Let stand at room temperature.)

Place spinach in large bowl. Toss with enough vinaigrette to coat.
Season with salt and pepper. Fill radicchio leaves with spinach.
Top with grilled onions. Pass remaining dressing separately.

Bon Appétit
June 1996

Reviews can be found here: http://www.epicurious.com/recipes/recipe_views/views/2222