Interior window sills with shadow gap

Hello everyone,

I would like to have interior windowsills with shadow gaps in my house. Originally, I wanted to use "Helopal linea," but both my plasterer and carpenter advised against it. Both said that installing it on plastered walls is extremely difficult and they could not guarantee a clean result.

Now I have been looking for alternatives. During this, I discovered interior windowsills with pre-assembled shadow gap profiles. According to my carpenter, installation should be trouble-free. However, I am skeptical about the HDF material they are made of. My clear preference would be cast marble.

Therefore, my question now is: Is anyone in this forum aware of where I can obtain the type of shadow gap profiles shown in the attached picture? Or does anyone know of a corresponding product made of cast marble with pre-assembled profiles?

Many thanks!
Clemens

Show me a picture of what something like that is supposed to look like "installed" - I can't imagine anything like that. Shadow gap between "what"?

Thank you for the feedback.
It should look roughly like this when integrated.

You get the same shadow if you let the windowsill without a joint project about 2 cm into the room. The main difference would be that significantly more installers could do that effortlessly.

You get the same shadow if you let the windowsill protrude about 2 cm into the room without a joint. The main difference would be that significantly more installers could do that flawlessly.

Unfortunately, this option is not an option for me. Flush with the wall is a basic requirement for optical reasons.

But Helopal. To my knowledge, they do offer accessories or profiles exactly for this shadow gap.