Cook the macaroni per package directions. Be sure to salt the water before cooking.
While the macaroni is cooking, melt the butter in a saucepan and sauté the garlic, thyme, jalapeno pepper, and smoked paprika for about a minute.
Add the onions and continue cooking for about a minute more.
Next, add the flour and whisk until blended. Gradually add the milk and bring it to a boil, simmering and stirring until the mixture thickens.
Remove about ¼ cup of the mixture. Let it cool for a few minutes before slowly whisking in the egg so it doesn't curdle.
Dump the tempered egg back into the pan and mix well to incorporate all ingredients. Stir in more than half of the cheese, leaving some to sprinkle on top.
Drain the macaroni, add it to the sauce, and stir until coated.
Add the mustard and white pepper. Taste it and adjust the seasonings as needed.
Transfer everything to a greased 2-quart baking dish or a 13"x9" baking dish.
Sprinkle the remaining cheese on top. Bake, uncovered, at 350℉ (180℃) for 20 -30 minutes or until heated through.