Pimento Cheese Potato Gratin

Ingredients

• 3 tsp. salt, plus more to taste
• 1 1⁄2 lb. Yukon Gold potatoes, peeled and sliced into 1⁄4-inch thick rounds
• 3⁄4 cup heavy cream
• 3 shallots, finely diced (scant 1⁄2 cup)
• 1⁄4 tsp. crushed dried red chile flakes
• 1⁄2 tsp. freshly ground black pepper
• 1 (9-oz.) jar roasted red peppers or piquillo peppers, with their liquid
• 8 oz. extra-sharp cheddar cheese, coarsely grated (about 2 cups)