Preheat your oven to 375°F and lightly grease a 9×13-inch baking dish.
Prepare the cheese sauce: melt butter in a large saucepan, whisk in flour, cook for 1 minute. Gradually add milk, simmer until thickened. Stir in cheese, garlic powder, salt, and pepper until smooth.
Mix the cooked pasta with the cheese sauce, then pour into the prepared dish, smoothing the surface.
Unroll the crescent dough onto a floured surface, cut into 8-10 strips about 1 inch wide. If perforated, press seams together first.
Shape each strip into an arch resembling a rib bone, tapering ends for realism. Larger middle ribs, smaller ends.
Arrange crescent “ribs” evenly over the mac and cheese, about 1 inch apart, pressing edges into the dish. Brush with beaten egg if desired.
Sprinkle with black sesame seeds, paprika, or edible charcoal for a bone-like appearance.
Bake uncovered for 20–25 minutes until golden and cooked through.
Allow to cool 5–10 minutes before serving.