For years, I have had trouble getting potato dishes "just right." A couple of days ago, I got into it deeper, did some experimentation and some research as I encountered trouble.
This applies to funeral potatoes, scalloped potatoes, potatoes au gratin, etc. It does not apply so much to brazing, pot roasts with potatoes, or at all to baking potatoes.
We think potato dishes are easy, don't require artistry so much, no-brainer, right? That's not been my experience. So, I have written this little thesis based on what I learned coupled with research into the unsatisfactory outcomes.
Slightly relevant, but off-subject tangent:
In the last couple of years, googling has gone from a fairly dry activity that resulted in getting a list of websites that might contain useful information to getting very pointed answers that are useful. In my professional use of AI over the last couple of years, I have learned that you get better information when you ask more pointed questions of an AI. This is completely opposite the best way to google for information back in the day when only keywords were what you should include.
When you use the Google search engine, the AI that's replying to you is called Gemini. Gemini takes your question, uses an intermediate component, a sort of "mixture of experts" to decide what language models to invoke as it formulates your answer. (And, pretty dang fast too!) "Language models" are the sort-of experts on various fields; they are mostly just data with high-speed wiring simulating neural networks. They are not actually "intelligent" however we like to hype them as such.
So, I asked a bunch of questions about what I was doing, what wasn't working, etc. and got lots of good information to back up (or refute) my own assertions.
Okay, back to business here...
Potatoes need intense, trapped steam to bake through when submerged in a heavy sauce. If not tented and sealed tightly around the edges of the pan with aluminum foil, the moisture escapes and, without that trapped steam, the potatoes essentially sit in a dry bake and stay hard. Pyrex baking dishes aren't optimal for sealing foil to them despite that they are the very "go to" for this purpose. Because we use "one-shot, throw-away" foil pans we buy on purpose at the store to make funeral potatoes, we usually fare much better. But, when cooking for the family, or on the spur of the moment, you're going to be using Pyrex, am I right?
Blanching or par boiling is helpful to accelerate the cook time, but if the dish you're making requires the potatoes have a particular form, it complicates things because you risk over-cooking too much (to mush) if inattentive or distracted. You might make the potato too hot to handle/place/position/etc., it introduces an extra step, dirties an additional pot. Worse still, par boiling removes starch that you probably wanted to retain texture-wise in your final dish.
Additionally, starch will not swell or soften if in an acidic environment. Sour cream is highly acidic. When raw potato slices are coated in a sour cream-heavy sauce, the acid chemically tightens the potato molecules, making them take significantly longer to break down and soften than they would in standard heavy cream or milk. Did you use sour cream because it's what you had on hand or because it's cheaper than heavy cream or because it's more luscious than mere milk?
Potato dishes involving cheese are complicated in that, if you expose the recipe itself directly to the oven by removing the foil only to discover after the 1 hour backing time that they are still too under cooked even to be called al dente, what to do? You don't want to brown or burn the cheese even more--the fricot is just perfect and a longer bake will destroy that.
Do not drop the temperature from, say you were baking at 375°, to something like 325°. This will slow the cooking process even more and you'll just "never" get the dish baked. Instead, do this: