In a large pan of boiling salted water, cook the macaroni until al dente. Drain well, shaking off any excess water.
Brush mini muffin tins (48 mini-cups total) with butter. Sprinkle with 2 tablespoons of the Parmesan.
In a large saucepan, melt the 1 1/2 tablespoons of butter. Whisk in the flour and mustard over moderate heat for 2 minutes. Whisk in the milk and cook, constantly whisking, until boiling, about 5 minutes. Add the cheddar and American cheeses and whisk until melted. Mixture will be very thick. Remove from heat, and whisk in the egg yolk and paprika. Fold in the macaroni.
Spoon slightly rounded tablespoons of the macaroni into the prepared muffin cups, packing well. Sprinkle the remaining Parmesan on top.
Bake for about 10 minutes, until golden and sizzling. Let cool for 5 minutes. Carefully loosen the mini macs, remove from pan to a platter, and serve.
These can be prepared through Step 4 and refrigerated overnight.