Try this ... boil pasta first till al dente and put in an oblong buttered baking pan and set aside...then in separate pan, melt the butter in the pan and add the flour and cook it a bit to form a roux do not let it brown for mac and cheese....then begin adding milk slowly and stir with a wire balloon whip to smooth out the lumps. After you add all the milk continue stiring on lowish to medium heat. When you see it getting thick like a white sauce (but not too thick) put in the shredded cheese. I would say use a standard brand like kraft medium cheddar or a cheddar jack cheese mix.) Turn off the heat immediately you do not even need to cook it with the cheese in there as it will melt by itself. I usually do not add all the cheese then I add some as I am assembling the dish... Then pour the cheese sauce on your cooked pasta which is in the pan and mix it so it is evenly distributed in the baking dish, incorparating extra cheese to make it cheesier....put sprinkled cheese on top and panko bread crumbs. I like to add a bit of paprika to the top too (I tend to put paprika on everything I bake). Then bake in the oven until top is brown and crusty...the inside will be creamy cheesey though. I like to use a mix of cheese and include parmesan too my favorite...cheddar of course. I do not see how this can fail. I actually do not even use a recipe anymore for mac and cheese.
In my opinion, you should not have to resort to immersion blenders, powdered cheese or chemicals. I think you might be putting the cheese in too early and that might be the problem. Try it and see.
Toria
"I like this place and willingly could waste my time in it" - As You Like It,
W. Shakespeare