Baked Pasta Shells with Sausage and Greens

Name: Baked Pasta Shells with Sausage and Greens
Ingredients: ¼ cup plus 1 Tbsp. extra-virgin olive oil; 1 lb. sweet or hot Italian sausage, casings removed; 6 garlic cloves, coarsely chopped; 1 Tbsp. finely chopped sage, plus 10 leaves for serving; ½ tsp. crushed red pepper flakes; 2 cups half-and-half; 12 oz. Fontina and/or aged cheddar, coarsely grated, divided; 1 lb. ridged medium pasta shells (such as lumaconi) or large tube pasta (such as rigatoni); 1 bunch broccoli rabe, stems cut into 2 pieces, leafy ends left long