1.Preheat oven to 400°F. Coat eighteen cups of two 12-cup muffin tins with cooking spray.
2.In large pot of boiling salted water, cook elbows according to package directions until al dente. Drain, rinse and return to pot.
3.Meanwhile heat oil in large skillet, preferable cast iron, over medium heat. Add garlic and onion and cook, stirring often, until softened and just starting to brown, 2 to 4 minutes.
4.Stir in 1 cup of milk and heat until milk is just starting to steam but is not bubbling. Remove from heat and sprinkle flour over milk; stir until smooth. Gradually whisk in remaining 1 cup milk; continue whisking, scraping along edges of skillet, until smooth, 1 to 2 minutes.
5.Return skillet to low heat and cook, stirring often, until mixture bubbles and thickens, 2 to 3 minutes. Stir in both cheddars and gruyere cheese.
6.Pour cheese sauce over macaroni, stirring to coat. Stir in half of Parmesan, truffle oil and salt. Allow mixture to cool for 5 minutes.
7.In small bowl, beat egg and half-and-half; stir into macaroni mixture.
8.Divide mixture among eighteen prepared muffin tins. Top each "cupcake" with stuffing or breadcrumbs and remaining Parmesan.
9.Bake for 18 to 20 minutes or until golden brown on top and heated through. Let cool for about 15 minutes before serving.