Grilled Panini With Portabello Mushrooms And Red Onions

Directions

1. For the Basil Vinaigrette: Combine the basil leaves, vinegar, garlic, mustard, salt and pepper in a mini-processor. Add in the oil; mix well. (This can be made a few hrs ahead and left at room temperature.) Set aside 3 Tbsp. plus 2 tsp. for the mushrooms and onions.
2. For the Panini: Heat the oven to 375 degrees. Brush mushrooms clean; wash them only if they're especially dirty by placing them in a colander and quickly rinsing with cool water. Dry with paper towels. Trim off any bruised spots, tough or possibly dirty ends or possibly edges. Trim mushroom stems and use a melon baller or possibly a grapefruit spoon to remove the gills.
3. Brush both sides of the mushrooms with 2 Tbsp. plus 2 tsp. of the reserved vinaigrette. Arrange the mushrooms in a single layer on a baking sheet.
4. Place the onion slices in a bowl; toss with the remaining reserved Tbsp. of vinaigrette. Mound them on the baking sheet with the mushrooms. Bake till the mushrooms are tender and the onions are cooked down but still retain some texture, about 25 to 30 min.
5. Set them aside till cold sufficient to handle, then cut the mushrooms on the bias into 4 to 5 slices. Coarsely chop the onions. (This can be done several hrs ahead; keep at room temperature.)
6. To assemble, brush some vinaigrette on the bread. Divide the onions proportionately and spread them on 4 slices. Arrange the arugula on each to cover, dividing proportionately. Layer the cheese over each. Fan each portabello, overlapping, over the cheese. Season with salt, pepper and red pepper flakes. Close the panini. (This can be done several hrs ahead.)
7. Spray oil on a large grill pan or possibly frying pan. Heat till warm over medium heat; lightly spray oil on the outer surfaces of the panini. Cook, covered, till browned on one side, 3 min; turn, gently compress, then brown the other side, about 3 min more. Let rest 5 min before cutting in half. Serve warm.
8. This recipe yields 4 servings.