Okra Mac and Cheese with Andouille Sausage

Name: Okra Mac and Cheese with Andouille Sausage
Ingredients: 1 pound uncooked short pasta (such as casarecce, cavatappi, or penne); 1/4 cup olive oil , divided; 2 pounds fresh okra , sliced into 1/2-inch pieces (about 7 1/2 cups); 1 pound andouille sausage , cut into half-moons (about 3 cups); 1 small yellow onion , finely chopped (about 1 cup); 3 tablespoons finely chopped garlic (about 8 cloves); 1/4 cup unsalted butter , plus more for greasing; 1/4 cup all-purpose flour; 3 cups evaporated milk; 2 tablespoons Creole seasoning (such as Zatarain’s); 2 teaspoons dry mustard; 1/2 teaspoon ground white pepper; 8 ounces sharp white cheddar cheese , shredded (about 2 cups), divided; 8 ounces Gruyère cheese , shredded (about 2 cups), divided; Chopped fresh parsley and sliced scallions , for garnish