Portobello Mushroom Sandwiches with Basil Aioli

4 large portobello mushrooms, wiped clean

3 cloves garlic, cut into thin slivers

leaves from 1 sprig fresh rosemary (optional)

3 tablespoons extra-virgin olive oil

3 tablespoons balsamic vinegar

1 large fresh, ripe tomato, cut crosswise into 1/2-inch slices

salt and freshly ground black pepper

4 onion rolls, hamburger buns, or a 5-inch section of baguette, split

Basil Aioli or mayonnaise

Preheat the grill to high.

Cut the stems off the mushrooms flush with the caps. Using the tip of a paring knife, make tiny holes in the caps, and insert the garlic slivers and rosemary leaves (if using). Combine the oil and vinegar in a small bowl and whisk to mix. Generously brush the portobello caps and tomato slices with this mixture and season with salt and pepper.

When almost ready to cook, preheat a vegetable grate for 5 minutes. Arrange the portobello caps, rounded side down, and the tomato slices on the hot grate and grill, turning with a spatula, until nicely browned and soft, 3 to 6 minutes per side. Brush the vegetables once or twice as they cook with the oil and vinegar mixture.

Spread the insides of the rolls, or bread with Basil Aioli or mayonnaise. Add the grilled vegetables and serve immediately.

Serves 4.