Chef John's Tuna Noodle Casserole

3 tablespoons unsalted butter

 

½ cup finely diced yellow onion

 

1 ½ teaspoons kosher salt, divided

 

3 tablespoons all-purpose flour

 

4 cups cold milk

 

1 cup shredded white Cheddar cheese

 

1 (12 ounce) package dry egg noodles

 

2 (5.5 ounce) cans tuna packed in olive oil, drained and crumbled, or to taste

 

¾ cup frozen peas, thawed and drained

 

1 pinch cayenne pepper

 

¼ teaspoon freshly ground black pepper

 

¼ teaspoon Worcestershire sauce

 

½ cup plain bread crumbs

 

½ cup grated Parmigiano-Reggiano cheese