6 tablespoons plus 1 teaspoon extra-virgin olive oil
1 head cauliflower (about 1 1/2 pounds)
1 teaspoon salt
1/4 teaspoon pepper
1/4 teaspoon sugar
1 pound short pasta (such as fusilli, rotini or campanelle)
1/4 teaspoon red pepper flakes
2 – 3 tablespoons juice from 1 lemon
1 tablespoon fresh parsley leaves, chopped
2 ounces Parmesan cheese, grated or shredded (about 1 cup)
1/4 cup chopped walnuts, toasted
Adjust an oven rack to the middle position, place a large rimmed baking sheet on the rack, and heat the oven to 450 degrees.
Cut one 12-inch sheet of foil and spread it flat on the counter. Place the garlic heads, cut-side up, in the center of the foil. Drizzle ½ teaspoon olive oil over each head and fold up the sides of the foil to seal well. Place the foil packet directly on the oven rack (not on the preheating baking sheet) and roast until the garlic is very tender, about 40 minutes. Remove the foil packet from the oven, open the foil and set it aside to cool.
While the garlic is roasting, trim the outer leaves of the cauliflower and cut the stem flush with the bottom. Cut the head from pole to pole into 8 equal wedges and then cut the cauliflower into large bite-sized pieces. Place the cauliflower in a large bowl; toss with 2 tablespoons oil, salt, pepper, and sugar.
Remove the hot baking sheet from the oven. Carefully transfer the cauliflower to the baking sheet and spread into an even layer. Return the baking sheet to the oven and roast until the cauliflower is well browned and tender, 15 to 20 minutes
While the cauliflower roasts, bring 4 quarts of water to a boil in a large pot. Add 1 tablespoon salt and pasta; cook until al dente. Squeeze the cooled, roasted garlic cloves from their skins into a small bowl. Using a fork, mash the garlic to a smooth paste, then stir in red pepper flakes and 2 tablespoons lemon juice. Slowly whisk in remaining 1/4 cup oil.
Drain the pasta, reserving 1 cup cooking water, and return the pasta to the pot. Add the chopped cauliflower to the pasta; stir in the garlic sauce, ¼ cup cooking water, parsley, and ½ cup cheese. Adjust the consistency of the pasta with additional cooking water and season with salt, pepper, and additional lemon juice to taste. Serve immediately, sprinkling with remaining ½ cup cheese and toasted nuts.