Pappardelle with Jammy Onion Ragu

Melt 5 tablespoons butter in a very large, deep, heavy-bottomed skillet or an 8-quart Dutch oven over medium heat. Add onions and 1/4 teaspoon salt. Toss to coat in butter. Cook, covered, stirring occasionally, until onions are tender, about 15 minutes. Increase heat to high. Cook, stirring constantly, until onions start to brown, 3 to 5 minutes.

Reduce heat to medium and add garlic; cook, stirring, until fragrant, about 1 minute. Add tomato paste. Cook, stirring constantly, until mixture begins to darken, 1 to 2 minutes. Add wine to skillet, then use a wooden spoon or spatula to scrape up any browned bits from bottom of pot. Simmer for 2 minutes.

Add broth, bay leaves, thyme, crushed red pepper, and cloves. Bring to a boil. Reduce heat to low; simmer, stirring occasionally, until liquid is reduced and onions are jammy, with just a bit of liquid at the edges of skillet, about 25 minutes. 

While sauce simmers, cook pasta according to package directions. Drain, reserving 1/2 cup cooking water. Remove sauce from heat. 

Remove  and discard bay leaves. Stir in sun-dried tomatoes, vinegar, black pepper, and remaining 2 tabelspoons butter and 1/2 teaspoon salt. Stir cooked pasta into warm sauce, adding reserved pasta cooking water a little at a time until sauce is desired thickness. Serve with Parmesan cheese and garnish with thyme.