Sounds like you should have bought a corner sink/pedestal or other for the space.

Have you tried your Google?

We're not seeing the powder room space or dimensions.

A powder room needs only a place to wash hands, a mirror, hang a roll of toilet paper for the potty, and have a soap pump at the water supply.

Show the space in a drawing, walls, window if there is one, where and how large the entry, exact feet and inches for all.

There are very functional, less expensive ways to meet the needs than a cabinet maker.

16" all

https://www.thebathoutlet.com/Bathroom-Vanities/product-search/50131?utm_source=google&utm_medium=ppc&utm_campaign=shopping-vanities&gad_source=1&gad_campaignid=22130998715&gclid=Cj0KCQjw8KrFBhDUARIsAMvIApYucm_D6lijOQXRFewQewAAcrbX8CANWJJNE22aGbW2rUZz1Kdw_PgaAndwEALw_wcB

personal preference but when space is tight in a PR I like a pedestal sink over a tiny vanity

Get the sink first or it's likely the cabinet will not be able to accommodate the sink.

I would not do a vessel sink, anywhere!

I have an 18" deep vanity Top, the vanity itself is 17" deep and it has a sink that is 10-1/2" front to back with plenty of room for a deck mounted faucet behind.

My top is custom too, made out of Corian as is the sink but not because I could not find a sink to fit but because I wanted a fully integrated sink and the top coved around the top where it met the wall tile. It was not all that much more to have it made all together than buying a sink and then getting a separate top.

There are so many sinks out there and usually you can set the parameters for size to help you search. Actually for a long time the Standard depth for a vanity counter was 21" not 24". Things just keep getting bigger and bigger. But they still make sinks to fit in smaller vanities. I would not do a vessel sink.

This sink ( link below )will fit in an 18 d x 24 w cabinet.

Beyond that? Show the room dimensions.

Make a drawing.....walls, entry etc

Bowl dimensions: 16" L x 9-7/8" W x 5-1/2" D. Overall dimensions: 18-1/8" L x 12" W x 6-7/8" D.

https://www.myknobs.com/pdp/hr-porcelain-bathroom-sink-8909/hr-h8909wh/hardware-resources-16-l-x-9-7-8-w-white-rectangular-undermount-porcelain-bathroom-sink-with-overflow?gad_source=1&gad_campaignid=17339320759&gclid=Cj0KCQjw8KrFBhDUARIsAMvIApafcFyvkH6o_XZbWp3xWqIp_SrVYPQaiEBiw-vccSgQvzM_n-vAz-saAo9UEALw_wcB

https://www.signaturehardware.com/destin-narrow-rectangular-undermount-bathroom-sink---white/484567.html?utm_source=google&utm_medium=cpc&utm_campaign=_21021715600&utm_content=_162442288481_690722842774_c&gad_source=1&gad_campaignid=21021715600&gbraid=0AAAAAD_wsC07fyTpz0Sis1df7jpoILQLv&gclid=EAIaIQobChMIr8XA5NWjjwMVs19HAR05cjuXEAQYBCABEgLPGPD_BwE

Having a long narrow bathroom,I bought the Lillangen sink from Ikea.
We wallmounted it and got a rather nice one handed tallish faucet ,also Ikea.
They also sell a matching vanity,but I chose to fit various wire baskets and shelves underneath and sewed a two panel cloth curtain to conceal all neatly.I sewed two sets of panels to coordinate with different shower curtains.
The panels are hemmed,and i threaded through thick copper wire bent at corners and hooked in the middle and screwed to the wall directly under the sink.
The entire set up is easy to access and to swap out the panels.
The sink itself has a ledge for soap bottle and nail brush,it is small but sufficient for a powder room.
Do get the sink first,and work from there.
Vessel sinks seem to have a poor reputation and are an extra cleaning chore.

Thanks all. @palimpsest could you share the link to the sink top or a picture of your vanity please?

Vanity and top

It's a tiny bathroom, 4 ft wide. 1965 house, so it's teak ply with a partial inset door. The Corian fabricator made the shower base, the top and the waste basked in the middle.

The lowest drawer is short and stops before it hits the toilet. The middle drawer goes over the top of the toilet seat.