I have created custom page layout for my other 'normal' pages.
However i can't find how to set my blog to use my page layout? Or any other page layout for that matter.
Is it possible to change a the page layout that a blog uses?
Since page layout functionality belong to the publishing infrastructure, you can try activating the Publishing Infrastructure feature, this will give you the ability to change the page layout on your blog site and after changing it, deactivate the Publishing feature. I think this will do the trick, but keep in mine that Microsoft doesn't support this scenario.