I don't know much about football, but I do know that if you're stuck watching a game at your friend's house, for no discernible reason other than to see New York teams get creamed, you'll be much happier if you've got a bag of chips and a bowl full of cheese dip.
Cheese dip wasn't really a thing in my household when I was a kid. I was first introduced to it by the mother of one of my American friends, who, crucially, had access to the magic that is Velveeta. One moment, we were settling in to watch a bootleg VHS of The Mighty Ducks, and the next, there I was, sticking a chip into an unnaturally yellow pool of hot cheese flecked with bits of jarred salsa. The rest, as they say, is history.
What I didn't know at the time was that you don't need Velveeta to make a smooth cheese dip; all you need, as Kenji discovered years ago, is a little bit of cornstarch and some evaporated milk, and you can transform most cheeses from their semisolid state into a pourable consistency.
The reason Velveeta melts so readily into a puddle of uniform-seeming goo is that it includes sodium alginate, an emulsifying salt that's extracted from brown algae. (It performs a function similar to that of sodium phosphate, the emulsifying salt first stumbled upon by James Kraft circa 1912, which paved the way for the Kraft process-cheese empire.) Basically, sodium alginate helps the natural emulsifiers contained within cheese (cheese, after all, is a gel),* creating an emulsion that can survive heating beyond the temperatures at which a cheese's emulsion will normally break.
From Modernist Cuisine: "The casein proteins in milk coagulate to form a gel; they then settle out as curds. This process occurs at the outset of all cheese making. The gel traps the fat droplets in the milk, turning it into a solid emulsion. The solid gel makes cheese a very stable emulsion unless it is heated sufficiently to melt the gel, at which point the emulsion breaks."
If your goal is to produce a stable liquid emulsion with cheese, there are several routes you can take. In one of his two baked macaroni and cheese recipes, Daniel uses sodium citrate, a common emulsifying salt in the modernist pantry. Make a solution of it by whisking it into water or milk, then simply melt cheese into the solution; the sodium citrate will help keep the emulsion stable, just as sodium alginate does in Velveeta. You can also use Kenji's method for making cheese sauce, which relies on the same interplay between starch, liquid, and cheese as his three-ingredient, 10-minute macaroni and cheese recipe.
To increase the stability of the final emulsion, Kenji adds evaporated milk to the mix, which contributes a high volume of milk proteins without adding too much water. To get an idea of how proteins add stability to an emulsion, think of mozzarella, a low-fat, high-moisture, high-protein cheese. It takes very high temperatures to get mozzarella's fat and water to separate out. Compare that to cheddar, a high-fat, high-moisture, low-protein cheese, which starts leaking grease if you hold a piece in your palm for even a few moments.
Apart from the added milk proteins, the emulsion's stability depends on the inclusion of some kind of starch. In the macaroni and cheese recipe, that starch comes from the pasta itself, which is why we use only a bare minimum of water to cook the pasta, thereby increasing the concentration of starch in the cooking liquid. For a cheese dip or sauce, the addition of cornstarch serves a similar function: Starch molecules absorb water and expand, not only thickening the liquid phase of the sauce, but also physically preventing the proteins from binding into long, tangled strands and the fats from separating out and pooling. (Daniel uses cornstarch to play a similar role in his fondue recipe.)
The best way to incorporate the cornstarch is to coat the grated cheese in it, which ensures an even distribution and prevents the formation of annoying clumps. The great thing about this method is that by adjusting the ratios slightly, you can get different consistencies, without worrying about the resulting emulsion breaking. For dips, you'll want to use a tablespoon of cornstarch per pound of cheese, then add at least five ounces of evaporated milk. After that, you can use more evaporated milk to thin out your dip as much as you need.