It's probably just me, but are rouxes and bechamels just like REALLY hard to get right? I fuck em up every time, so I refuse to make cheesey sauces by hand anymore.
You can buy some sodium citrate off amazon. It's the emulsifier that makes american cheese and velveeta work, you'll get a smooth sauce with much better flavor than velveeta. Just google sodium citrate mac n cheese for a recipe, it's pretty easy to make.
Before I started caring about my waistline, I used to make giant batches of home made macaroni and cheese a few times a month. My recipe is simple, but I recognize it's also probably an abomination when compared to proper techniques, but here's the thing - it's easy, forgiving, and it works!
Forgive my lack of measurements. I'm going to try, but I've just winged it for years.
3-4 cups of milk in at least a 2qt saucepan. Slowly heat to almost a simmer, stirring to keep the bottom from scorching. As it's heating, really mix about 1/2 cup milk and a couple fat tablespoons of flour. You want a good amout of flour, but loose enough to still be able to pour. When the milk is starting to ripple, slowly pour in the flour mixture while whisking.
This would technically be the hardest part. Don't add all the flour mixture yet. Flour thickens the most once it comes to a boil. Mix/whisk in about half, see how thick the mixture gets once it starts to bubble (watch for hot spatters!) When I make it I want like a gravy texture - not runny, not pudding, somewhere in between. Not thick enough? Add more flour mix. Too thick? Add a splash of milk. You just need it to bubble slowly for a couple minutes to achieve it's full potential.
Once you've gotten a decent texture (remember it will thicken a little more after cooling) take it off the heat. Add garlic powder, onion powder, whatever seasoning you want, just be careful with salt until you've tasted it with the cheese. Now that you've stirred it a bit, add your cheese and let the remaining heat melt it. Depending on if you're using shredded or cut a block into chunks, you may have to warm it a little on the heat if it gets too cold, but DON'T bring it back to a boil. There's a risk some cheeses might break if you do. Don't get it too hot and you should be good.
I fought with making a proper roux too many times. My "nobody knows what I'm doing alone in the kitchen" version was far easier (forgive me real chefs 😉.)
slowly add 1.5 cups milk and vigorously whisk it into the butter and flour mix (slowly is key here too fast and you'll end up with lumpy sauce)
Once all the milk is added you should have a smooth but thin sauce. Cook your sauce until it reaches a consistency that you want then add your cheese (I add 100-150g of parmesan to this for alfredo or 150g of cheddar for mac and cheese sauce). Remember that the sauce will thicken more once you take it off heat.
Edit: Also spices are on you. Spice it however you like starting with at least some salt since the milk will take some salt away from the cheese.
Make sure you're whisking while you add the milk. Slowly adding the milk and whisking are the keys to making it smooth. Some people will even just add the milk 1/3 at a time. So add a half cup while whisking, get it integrated, then add another half cup, repeat til all the milk is in.