Don’t do interviews, do discussions

Others in the comments have expressed some legal concerns about "discussions" instead of Interviews, but I feel this is a hyperbolized fear based off a laypersons interpretation of US hiring law. The law requires you ask the same set of questions of all candidates, yes, but it reasonably understands that questions on past projects/work of course will never be the same, and these are legal and valid areas to go off-script.

So suppose in your situation you have a candidate and they talk about the project they worked on. To hear about their contribution, you ask (as you would all candidates):

"Tell me about a problem you encountered on this project that was particularly challenging from a technical perspective"

The candidate will tell you and likely their solution, and then you can start with the why's and how's.

"Why did you choose this approach? What are the benefits?"

"How did you arrive at this conclusion?" (you can further restate the question with "explain how you got to the idea that you needed to get here")

Make it a hard rule for yourself that you must be able to build the entire timeline and understand the candidate's role in that timeline. I find that even if it turns out they mostly were receiving orders from a more senior resource but could reasonably explain in their own words now why they ended up doing what they did, this is still a good candidate for me as they used available resources and took away a good lesson. If there is ambiguity, you can even just ask "why do you think your senior colleague had the right idea here?"

The idea of a discussion versus a checklist is you want to learn how a person thinks and how they approach issues. Even as a follow up to more factual check-list questions, "why" is very important as it helps you to understand the current state of the person. Just be honest with yourself that not everyone will have the same background and be honest on whether the "why" is relevant for the position. For example, some trivial linux kernel knowledge I would consider "nice to know", but it's by far not essential unless they're doing specific dev work on that field or claim to know it.

The other big catch you need to train yourself for is accepting that people will do things far differently than you do, even things that you consider wrong, but they work. The important part to focus on isn't about how close their answer is to yours, but to make sure you understand how and why someone reached that conclusion.

Why and how are very safe and legal questions as a follow up to a very straight-forward technical question.

I also just generally do not think that most people can even put together a 2-3 hour presentation of their past work that goes over well. Most of the time people can't really talk more than 30 minutes about past projects. That requires a whole different set of skills, which there are certain contexts where I'd value that more highly. But my initial impression is that if we set up our interviews this way, we'd also end up filtering out a lot of people who'd be great, since not picking the perfect project to demo basically dooms the entire interview to be a flop. With multiple interview types, you increase the chance that there's an interview they really shine in.

My view isn't that good programmers spend the majority of their time writing boilerplate code. But my view also isn't that the average programmer _isn't_ doing that.

I'd expect way more demonstrated knowledge for an interview in a higher level role than an mid level developer role. But the higher you go the less you actually need to demonstrate that. Why?

Making definitive statements about liability is not trivial. I can confirm that at some very large companies legal has banned this style of interview citing discrimination concerns. I'm not a lawyer, so I can't comment on whether they're call is more or less correct but it certainly doesn't seem settled.