2 tbsp. salted butter, melted
1 1/2 cups panko (Japanese-style breadcrumbs)
1 large egg
3/4 cup whole-milk ricotta cheese
6 tbsp. coarsely chopped fresh flat-leaf parsley, divided
1/2 tsp. kosher salt
1 cup mayonnaise (such as Duke’s)
6 oz. processed cheese (such as Velveeta), cubed (about 1 1/2 cups)
8 oz. sharp Cheddar cheese, shredded (about 2 cups)
2 cups whole milk
1 tbsp. finely chopped garlic (2 to 3 garlic cloves)
3 tbsp. all-purpose flour
3/4 cup chopped yellow onion (from 1 onion)
1/4 cup salted butter
12 oz. uncooked large elbow macaroni