Place peppers on a baking sheet and broil, turning, until skin is charred. Remove from oven and either place in a paper bag, or in a bowl covered with plastic wrap. After 10 minutes, peel peppers, seed, and cut into quarters.
Whisk together vinegar, maple syrup, mustard, garlic, salt, and pepper. Begin adding oil very slowly while continuing to whisk so dressing can emulsify.
Add more oil, still a little at a time, until desired taste is acquired.