I would say sorry for my English it's foreign for me. If you will find mistakes or typos please let me know))
I've saw the one instruction on youtube (Harry Potter DIY Tom Riddle's Diary | Lauren Fairweather Collab | Sea Lemon) and thought: Wow, I could do something like this but from real leather and simpler!
Step 1: Prepare Leather
I've thought that the cover with craft-papers block is more useful, because you can use this type of notebook in several time longer!
This step is simplest because you need not do anything manually) Just find the suitable piece of leather.
For this step we need the hard 4mm/10oz black leather and laser cutter.( Please find attached TomasRiddleDiary.cdr file with prepared model for laser cutting )
Step 2: Back Side of Cover
For making the cover more long-lived the back side could be covered by tokonole, for example. (it's a special coating for leather that make back side of the leather sleek)
Step 3: Prepare the Fastener
Time to time it's difficult to find the suitable fastener and I've found not bad variant where it could be found.
It can be taken from usual paper folder and you can separate it very fast. To buy paper folder is really simpler that trying to find the separate fastener.
Step 4: Mark the Place for the Fastener
Mark the place for fastener by ruler and awl. The fastener should be at the center of the cover.
Step 5: Make It Flex Where It's Needed
Mark (by awl and ruler) 2 verticals parallel lines on the inner side of the cover with distance between them little bigger then size of the fastener.
Use V-type or U-type cutter and ruler for making these lines deeper. The cover should be bend by these lines
Step 6: Good Angle Is a Hard Work
After bending knock out the new angles with rubber mallet. It will make them good-looking.
Step 7: Punch Holes
With mallet and hole puncher make a holes for the fastener installing
Step 8: Golden Words
Color the letters on the cover by golden dye, thin brush and needle.
It's slow process that need big accuracy.
And prepare some water and cotton disks - they can help to fix some mistakes of coloring.
Step 9: Cut the Extra
Now our cover have about 1 cm extra from each side (you should check it before cutting)
It could seem that you have more that 1 cm from left and right, but it could be a mistake, check it twice)
Step 10: Color the Edges
I've recommend to color the edges with special dye, it make them pretty and long-lived.
Step 11: Renew the Face of Cover
I'm using wax-based shoe polish like a finish. It's fast, easy and good-quality. But be careful, don't spoil you golden letters!
Step 12: Install the Fastener
With hammer and special tool install the fastener by the rivets.
Step 13: Install the Corners
Carefully install the corners by hammer or mallet. If the corner was installed incorrect you can reinstall it, but note: after several times it will be broken.
Step 14: Just Add the Paper Block
Put your prepared paper block inside the cover
Step 15: Enjoy!
And do not afraid if somebody inside the notebook will write to you... You know what you need to do in this case)