Prepare macaroni ahead of time, cooking 1-2 minutes less than the time on the box. Drain and rinse well. If cooking a day ahead, cover and refrigerate. Macaroni should not be wet when starting this recipe.
Preheat oven to 350°F. Liberally butter the bottom and sides of a 13×9” baking pan. Sprinkle with about 3 tablespoons of the bread crumbs; shake pan to coat bottom and sides. Place remaining bread crumbs (1/3 cup or so) in a small bowl and stir in 1/2 cup of the Romano cheese; set aside.
Measure milk. Add ANGOSTURA® aromatic bitters, salt, pepper and nutmeg; stir to dissolve salt. Place macaroni in a large bowl. Stir in milk mixture. Stir in the Cheddar cheese and remaining 1/2 cup Romano cheese. Let rest 5 minutes; stir again. Spoon into prepared baking pan and spread out evenly.
Sprinkle bread crumb/cheese mixture over macaroni. Bake uncovered 35-45 minutes until edges are browned. Let cool 20 minutes. Use a sharp knife to cut 35 squares (7 rows x 5 rows). Remove from pan with a metal spatula. Serve warm.