Spicy Baked Pasta With Cheddar and Broccoli Rabe

Name: Spicy Baked Pasta With Cheddar and Broccoli Rabe
Ingredients: Kosher salt; 1 lb. rigatoni, ziti, or fusilli; 8 Tbsp. extra-virgin olive oil, divided; 3 large leeks, white and pale green parts only, halved lengthwise, thinly sliced into half-moons; Freshly ground black pepper; 1 tsp. (or more) crushed red pepper flakes; 2 bunches broccoli rabe or 3 bunches baby broccolini, trimmed, coarsely chopped; 1 cup heavy cream; 12 oz. sharp white cheddar, coarsely grated (about 3 cups), divided; 1 cup chopped chives, divided; 1 cup coarse fresh breadcrumbs or panko (Japanese breadcrumbs)