Add macaroni and 1 tablespoon salt to a large pot of boiling water.

Cook until pasta is tender (not al dente; it should be fully cooked).

Drain and set aside.

In the same pot you used to boil the pasta, heat butter till it gets foamy.

Add flour, mustard and whisk to combine.

Continue whisking until the flour mixture browns slightly, about 1 minute.

Slowly whisk in milk and bring mixture to a boil, whisking constantly until the sauce starts to thicken. Reduce heat and whisking occasionally, let the sauce thicken to the consistency of heavy cream. Remove from heat and whisk in cheese along with the 1 teaspoon salt.

When cheese is melted, stir in pasta and cook till mixture is fully heated through, about 5 minutes.

Pour into a 9x13 tin or dish.

Combine the panko, cheese, paprika and butter. Sprinkle on top and bake 10-15 minutes to brown.