Labneh is a strained yogurt cheese similar to Greek yogurt. I've made Greek yogurt many times, and I was curious what the difference is with labneh that makes it more firm - firm enough to roll into balls. The difference, apparently, is the addition of salt. It draws out more of the whey. Here are a couple of how-tos:

Labneh at River Cottage
From themediterraneandish.com, very nice photos.

My method was pretty much the same as my Greek yogurt, except adding the salt first. Place a mesh sieve over a bowl, cover with a couple of coffee filters, pour the yogurt onto the filters, then cover with plastic wrap. Place in the fridge for 1-2 days.

A twist: I'm using homemade yogurt from heavy whipping cream.. My labneh is currently straining in the fridge; I'll report back how it turns out.