Translation:I want just the right amount of coffee.
That about gave me an aneurysm trying to figure out. "I want [a lot of] [just the right amount of] coffee." Okayyyyy. I wasn't sure if lagom can mean... something other than quantity? Like, "The salsa was lagom, not too spicy, not too bland"- something like that? Then I could see the above meaning "I want a lot of just the right blend (or to that effect) of coffee." That had me stuck for a while.