Onion Gratin

Name: Onion Gratin
Prep time: 15 min
Cook time: 45 min
Total time: 1 h
Cuisine: European, Mediterranean, French
Ingredients: 6 small onions; 2 tsp. olive oil, for brushing onions; 1 tsp. finely minced fresh rosemary (see notes); 2 T minced fresh thyme leaves (see notes); 1/2 cup mayo; 1 T + 1 tsp. fresh-squeezed lemon juice; 3/4 tsp. Dijon mustard; 1 1/2 cups Pizza cheese blend (see notes); 3 T grated Pecorino-Romano cheese (see notes); fresh ground black pepper to taste