Skirt Steak Salad with Mushrooms and Chipotle Aioli

6 MAIN-COURSE SERVINGS

AIOLI

1 cup mayonnaise
1/4 cup coarse-grained Dijon mustard
2 tablespoons white wine vinegar
1 tablespoon minced canned chipotle chilies*

STEAK

1/2 cup dark beer
1/4 cup olive oil
2 tablespoons chopped garlic
2 tablespoons red wine vinegar
1 teaspoon Worcestershire sauce
3/4 teaspoon hot pepper sauce (such as Tabasco)
2 pounds skirt steak, trimmed of fat

SALAD

2 red onions, thinly sliced into rounds
2 tablespoons fresh lemon juice
3/4 teaspoon coarse salt

3 tablespoons butter
1 large shallot, sliced
3/4 pound assorted mushrooms (such as crimini and oyster), sliced
1/4 cup Sherry wine vinegar
1/4 cup olive oil

10 ounces mixed baby lettuces

FOR AIOLI: Whisk all ingredients in small bowl to blend. Season dressing to taste with salt and pepper. (Can he prepared 1 day ahead. Cover and refrigerate.)

FOR STEAK: Whisk first 6 ingredients to blend in 13x9x2-inch glass baking dish. Add steaks to marinade; turn to coat. Cover and refrigerate at least 8 hours.

FOR SALAD: Combine onions, lemon juice and coarse salt in medium bowl. Let stand 1 hour; tossing occasionally