Roasted Garlic Parmesan Dressing

1 head garlic
½ teaspoon olive oil
1/3 cup champagne vinegar or white wine vinegar
2 teaspoons coarse ground mustard
½ teaspoon coarse salt
1/8 teaspoon freshly ground black pepper
½ cup extra-virgin olive oil or regular olive oil
¼ cup grated Parmesan cheese
1 teaspoon snipped fresh thyme

Preheat the oven to 425°F. Set the garlic head on its side on a cutting board. Using a sharp knife, cut about a ½-inch portion off the top part of the head. You should see most of the individual cloves revealed; if not, cut a little more off. Remove the loose papery peels from outside the head but do not take off all of the peel. Set the garlic head, top side up, in a custard cup. Drizzle with ½ teaspoon oil. Cover with foil.
Bake for 35 to 40 minutes or until garlic cloves are just soft when pierced with a sharp knife. Keep the garlic covered in the custard cup. Let stand on a wire rack until cool enough to handle (20 to 30 minutes).
Hold the garlic head on the bottom. Pinch bottom of head with your fingers to squeeze out the individual cloves. You may have to use a sharp knife to remove some of them.
Transfer garlic cloves to a blender. Add vinegar, mustard, salt, and pepper to the blender with garlic. Cover and blend until garlic is pureed and mixture is well combined. With the blender running on low to medium speed, slowly pour ½ cup olive oil through the hole in the lid, until dressing is well combined and thickened. Add cheese and thyme. Cover and pulse a few times just until combined.
Store dressing in a covered container in the refrigerator for up to 5 days. Whisk before serving if the dressing has separated (it shouldn’t separate as long as you blend well while adding the oil very gradually!). Dressing may thicken slightly when held longer than a day or two. If that happens, let dressing stand at room temperature about 15 minutes before serving; then whisk lightly.