- 1 1/2 cups white wine vinegar
- 1/2 teaspoon dried crushed red pepper
- 1 to 1 1/4 pounds red onions, thinly sliced
- 1/4 cup white wine vinegar
- 1/2 teaspoon Dijon mustard
- 1/2 cup crumbled blue cheese
- 4 hearts of romaine, each quartered lengthwise
- Crumbled blue cheese (for garnish)
Combine first 5 ingredients and 1/4 teaspoon coarse salt in medium saucepan. Bring to simmer over medium heat. Add onions and stir to blend; return to simmer and cook 2 minutes. Remove from heat; cool to room temperature, about 1 hour. Season with freshly ground black pepper and more salt, if desired. DO AHEAD Can be made 1 day ahead. Cover; chill.
Prepare barbecue (medium-high heat). Combine vinegar and mustard in bowl. Gradually whisk in oil. Season with coarse salt and pepper. Mix in 1/2 cup cheese.
Brush cut sides of romaine with olive oil, then sprinkle with coarse salt and pepper. Grill until cut sides are lightly charred, about 2 minutes per side.
Divide grilled romaine among plates. Top with vinaigrette, pickled onions, and blue cheese.