How to Make It
Cook reginetti according to package directions, adding table salt to the water. Drain pasta, reserving 1½ cups cooking water.
Place greens in a medium bowl. Toss with extra-virgin olive oil, lemon juice, pepper, and ½ teaspoon of the kosher salt. Massage for 2 minutes; set aside.
Heat olive oil in a large skillet over medium-high. Add guanciale, and cook, stirring often, until crispy, about 8 minutes. Drain on paper towels. Reserve 2 tablespoons hot drippings in skillet.
Reduce heat to medium. Add butter, thyme, garlic, and remaining ½ teaspoon salt; cook until butter is brown and toasty, about 2 minutes. Remove from heat; stir in 1 cup reserved cooking water. Return to medium heat, and simmer until sauce is slightly thickened. Add pasta, guanciale, cheese, and vinegar; toss to combine. Divide among 4 bowls, and top with greens mixture. Serve immediately.