I really like the concept(!)
I have been looking around for something like this, but selfhosted (any chance of it being opensourced?)

I learned about this site from a comment in another HN thread, thus did not read your "ShowHN" intro.
After visiting the site I could see what it was about (looks great), but I was not able to quickly find a description of the concept, thus what to expect, what is required etc.

So here's my feedback:
1. Promote the "ShowHN" blog post https://letscooktime.com/Blog/2022/04/29/hn-post.html (that I eventually found and read) to the "About" page thus let people like me answer the why, who, when etc questions.

2. Will the site be worth investing in for me?
If I start adding my own recipies there, can I export my data eg. to a local backup?
I know everything is being cloudified these days, but I'm old school and I know that nothing is for ever, even the good stuff.
It's possible that you loose interest in the project or (hopefully not) an accident occurs with the sideeffect of the site being terminated.
One comment in the other thread was about another similair site that was terminated, hence data was lost for the end users perspective.

3. Units
In Denmark (an likely in the rest of Europa) the use of "cups" is not de facto, in stead volume measurements are used (for small amounts) or weight (for large amounts).
Eg. in stead of 1/3 cup, then ~80ml would be used (well 78,66...) and when baking use 1kg of flour

Farenheit versus Centigrades
Is it possible to auto detect Farenheit and get it converted to Centigrades (or vice versa), either by auto detecting it and adding the other value in parens?
I typically see it refernced as '425°F' or 425F, so a regex might do the trick.

For large values (either via scaling the recipe or when a lot is needed for a normal serving)
Eg.: https://letscooktime.com/Recipes/Details?id=f9b12e31-c6fa-47...
'1 gallon (22656 grams) apple juice'
You should use the appropriate unit (> 1.000 grams => kg ...)
NB.: Something must be wrong with this conversion as 1 (us) gallon (~3,785 l) is not the equivalent of 22,656 kg, more likely ~3,785 kg), thus 'x6'.

Nitpick:
I prefer 'l' in stead of the 'L' as the unit of "litre" as it looks nicer: 'ml' versus 'mL'

4. User settings
I have yet to create an account so I am unaware if these features already exist, so sorry if this do not apply.
If one is not interested in the nutricion data, it would be nice to have a preference that turns displaying this off (both 'Nutricion Facts' as well as 'Nutricion by Ingredient').

Support "locale" or even better, allow a setting that defines how to represent values (again in dk/europa we use `.´ as a thousand seperator and `,´ as a decimal point - the US is opposit (I'd have to say wrong ;-)

5. Incorrect conversions
Something is wrong with the conversions.
In this recipe https://letscooktime.com/Recipes/Details?id=2474dfcc-7804-4e...
'350 ml' water is referred to as '35 grams' (where it should be 350 grams, thus 10x)

Also see the example in 3)

6. Index (original serving size)
It might be nice to know the original size if one often scales up as you'd like to know how much off the sizes might be (x2 - x4 is ok, but at x10 soe values might get off).
I know I can F5 to get the original recipe (which I presume is in the originally size asd it was entered).