IN THE REALM of vegetarian sandwiches, portobello mushrooms hold an honored place. Their wonderfully dense texture and earthy flavor give weight and heft to a sandwich, replacing the ubiquitous slice of cheese. If you want to take these sandwiches on a picnic, roast the mushrooms and prepare the dressing in advance, but assemble the sandwiches just before eating.

SERVES 4

INGREDIENTS

BLUE CHEESE DRESSING:

• ¼ cup buttermilk
• 3 tablespoons crumbled Roquefort or other blue cheese
• 2 tablespoons mayonnaise (reduced fat is fine)
• 2 tablespoons chopped fresh parsley leaves
• 1 garlic clove, peeled but left whole

MUSHROOM SANDWICHES:

• 4 large portobello mushrooms, trimmed and caps sliced ½ inch thick
• Extra virgin olive oil
• 8 large slices high-quality white or whole wheat bread
• 4 slices Vidalia or other sweet onion
• 1 ripe tomato, sliced
• 1 bunch arugula or watercress, stemmed, or 2 cups mesclun

INSTRUCTIONS

1. Make the dressing by combining the buttermilk, cheese, mayonnaise, parsley, and garlic in a blender or food processor. Process until thick and fairly smooth. Set aside at room temperature to let the flavors develop.
2. Preheat the oven to 500°F. Lightly oil two rimmed baking sheets.
3. Make the sandwiches by lightly brushing both sides of the mushroom slices with oil. Arrange in a single layer on the baking sheets.
4. Place the baking sheets side by side in the oven. Roast for about 10 minutes. Turn and roast for about another 10 minutes, until the mushrooms are completely tender when pierced with a fork. (If the baking sheets do not fit side by side, place one on the middle rack and the other on the bottom rack and rotate them once or twice during the roasting process.) Remove from the oven but leave the oven on.
5. Place the bread directly on the oven rack and toast briefly.
6. To assemble the sandwiches, spread the dressing on the bread. Arrange the mushrooms on 4 slices. Add an onion slice to each. Top with the tomato and greens. Cover with the remaining slices of bread. Cut in half, if desired.
7. Serve at once.

NOTE:

• Mushroom Steak Sandwiches with Goat Cheese Dressing: Replace the blue cheese in the dressing with mild fresh goat cheese, such as Montrachet. Proceed with the recipe as above.
• Blue Cheese Dressing Notes: The blue cheese dressing can be made several days in advance and stored in an airtight jar in the refrigerator. In fact, the dressing can be made in double or triple batches and used as a salad dressing. It also makes a great dip for raw vegetables.