Savory Mac and Cheese Cake

Name: Savory Mac and Cheese Cake
Ingredients: 1 1/4 cups plain yogurt; 2 large eggs; 1 teaspoon kosher salt; 1/2 teaspoon freshly ground black pepper; 1 teaspoon white sugar; pinch cayenne; 1 cup plus 2 tablespoons self-rising flour (or all-purpose flour plus 1 1/2 teaspoons baking powder); 6 ounces grated cheddar cheese, divided (5 oz. for the batter and 1 oz. for the top); 2 tablespoons sliced green onions, plus more to garnish if desired; 1/4 cup melted butter; 1 cup dry elbow macaroni; 1/4 cup reserved pasta water (not shown in video)