- 1/2 sweet onion, quartered
- 1/2 pound tomatoes, halved crosswise
- 1 large green bell pepper, halved lengthwise and seeded
- 1 fresh Charleston hot or habanero chile, halved
- 1 tablespoon olive oil
- 1 1/2 tablespoons finely chopped garlic
- 1/2 teaspoon kosher salt
- 2 cups mayonnaise
- 1/2 teaspoon black pepper
- 1 to 3 teaspoons white-wine vinegar, or to taste
Preheat oven to 400 degrees F.
Toss onion, tomatoes, bell pepper, and chile with oil in a shallow (1-inch) baking pan and arrange vegetables, cut sides down, in 1 layer. Roast, turning onion once or twice, until vegetables are charred and tender, about 20 to 25 minutes.
Mince garlic and mash to a paste with kosher salt. In a bowl, blend together mayonnaise, garlic paste, and black pepper. Add chile, about 1/4 at a time, tasting for desired heat. Stir in tomatoes, bell pepper, onion, and vinegar.
Aioli can be made 1 day ahead and chilled, covered.