Ribs:
2 tablespoons olive oil
2 1/2 pounds beef short ribs
2 teaspoons kosher salt, plus extra for seasoning
1 teaspoon freshly ground black pepper, plus extra for seasoning
1 onion, roughly chopped
4 cloves garlic, peeled and smashed
2 (4-inch) sprigs fresh rosemary
2 cups red wine, such as pinot noir
2 cups beef broth
Filling:
3/4 cup milk
1/2 cup heavy cream
1 1/2 cups grated Pecorino Romano (6 ounces)
1 cup shredded mozzarella (4 ounces)
1 (10-ounce) packet frozen spinach, thawed, drained, and squeezed of excess liquid
1/4 cup chopped fresh basil
2 cloves garlic, minced
1 teaspoon kosher salt, plus extra for seasoning
1/2 teaspoon freshly ground black pepper, plus extra for seasoning
12 lasagna noodles (about 10 ounces)
Butter, for greasing baking dish
1 (25-ounce) jar marinara sauce
1/2 cup freshly grated Parmesan
Olive oil, for drizzling