How can I make my french fries crispy? [duplicate]

Some restaurants have larger fries that are super crispy. The outside layer is hard and thick.

image: https://qualitygreens.com/recipes/recipe/160/Thick_Cut_Fries/

I wanted to reproduce this for years with no success. I tried countless sophisticated recipes from the internet but they never resulted these very crispy fries, I either got brown and soft fries, or regular fries.

The problem:

My problem is that I never could get my fries to be crispy. Most recipes are concerned by the fries being soft on the inside and crispy on the outside simultaneously. My fries were always soft on the inside but never crispy on the outside.

Most recipes pre-cook or pre-fry the potato to get the softness. To me, this would suggest that the crispiness is achieved with a high-temperature fry. This contradicts my experiences. A high temperature short fry always resulted my fries getting golden (and then brown if left for too long) while remaining soft. However, I could achieve regular crispiness if I used a low temperature long duration frying. This is the opposite of what should happen according to the recipes' logic.

What could be my problem?

What I have tried:

• Normal pan frying and frying while submerged in excessive ammouts of oil.
• As mentioned, both low and high temperature frying.
• All sort of pre-cooking and pre-frying. No difference in crispiness, while the inside is soft as usual.
• Keeping the sliced potatoes in water for a few hours. Water regularly replaced for better solvation.
• Various oils. Rapeseed and sunflower was tried, no differences observed.
• Thin coat of cornstarch. No increase in crispiness, but the difference was observable.
• Various potato types. Both high and low starch potatoes were tried (A, B, and even C). The difference between various types was clear, but not in terms of crispiness, that was as usual. I'm the most surprised by the high starch (C) potato's indifference. Finding a high starch potato was very difficult, almost no supermarket has them where I live.
• Instead of frying, baking them in an oven at high temperature (240°C (464F)). This did yield the desired crispiness, demonstrating that it is possible, however oven-made fries cook very unevenly, with the sharp edges even turning into black coal. Cooker and oil frying is preferable.

Some more pictures: To aid in troubleshooting I made some pictures of my latest experiments. This time I was experimenting with very high temperatures. Pre cooked potato was fried in 210-180°C (410-356F) oil. The recipe I tried said 3-4 minutes of frying, but I did another batch until they turned gold-brown in 7-8 minutes.

Both batches had a very thin outer layer, and were normal-crispy at first, then became soft and paper-like after 3-5 minutes. Later, I did a conventional batch for benchmark, that was fried in 130-150°C (266-302F) for 25 minutes. It became a normal medium-crispy fries.

What could be my problem? Why can't I get good crispness?