Cook pasta until al dente.
Make roux with butter and flour.
Gradually whisk in milk.
Add cheeses and mustard powder.
Stir until melted and smooth.
Mix sauce with pasta.
Pour into baking dish.
Top with panko mixed with melted butter. This is your chance to make it look as good as it tastes! A little garnish goes a long way for presentation.
Bake at 375°F for 25-30 minutes. Every oven is a little different, so start checking a few minutes early. You're looking for a golden color and a wonderful aroma filling your kitchen.