Cook the shells in well-salted water until just past al dente, a little softer than you'd cook pasta for an Italian dish. Velveeta shells are tender. Drain but don't rinse, and don't toss with butter.

While the pasta drains, warm the evaporated milk, whole milk, and canola oil together in the same pot over medium-low heat. Whisk gently until just steaming.

Drop in the American cheese first. Stir until completely melted and smooth. The American cheese is doing the emulsifying work here.

Reduce the heat to low. Add the grated cheddar in two handfuls, stirring after each addition until smooth. Keep the heat low.

Stir in the salt, vinegar, and turmeric. Taste. The sauce should be mild and lightly tangy. If it's too sharp from the cheddar, add a splash more evaporated milk.

Add the drained pasta and fold to coat. Let it sit for one minute off the heat, and the sauce will tighten slightly around the shells and cling the way the box version does. Serve immediately.