Kosher salt
8 ounces medium pasta shells
2 tablespoons olive oil
2 garlic cloves, minced
¼ teaspoon red-pepper flakes
10 ounces fresh baby spinach, or frozen chopped spinach, defrosted and drained
1 (14-ounce) can artichoke hearts, drained and roughly chopped
2 cups heavy cream (1 pint)
4 ounces grated Parmesan (about 1 cup)
Black pepper
4 ounces grated mozzarella (about 1 cup)