1 lb. Pappardelle's Roasted Garlic Fettuccine
6 medium cloves garlic, divided
4 scallions bunches, green parts only, chopped
3/4 cup heavy cream
1/4 tsp. kosher salt
4 Tbsp. unsalted butter, divided
1-1/2 cups sweet peas
2 oz. thinly sliced speck (about 8 slices), torn into 2" strips
1 oz. grated Parmigiano-Reggiano cheese, plus more for serving
1/2 cup fresh mint, coarsely chopped
1 tsp. lemon zest, plus 1 tsp. fresh lemon juice (from 1 lemon)