These are so cute! They look comfy! Do you have the pattern?
A pattern, eh? Well, I kind of just measured it against my foot at I went, so there's not really a real pattern. This is, roughly, what I did:
With a fuzzy yarn that will hide errors (I used Bernat Boucle) and an appropriate hook:
ch 3, join to form loop
Rnd 1: 6 sc into loop
Rnd 2: 2 dc in each sc
Rnd 3: 2 dc in each dc
Rnd 4&5: 1 dc in each dc, do three dec evenly spread out
Rnd 6: 1 dc in each dc
Repeat Rnd 6 until it gets close to your ankle (stretch it a lot when measuring)
Once you're happy with how far it reaches, start working in rows. (So, pretend you're starting the next round, but don't finish it)
Each row: 20 dc
Keep making rows until it reaches the back of your heel (don't forget to stretch it when measuring). When you're happy with it (tight slippers are better with this pattern), finish off, cut a really long tail and use it to sew up the back.
I'll eventually be making more of these soon, so if you want, I can take pictures next time.
Really, it's just: start with a small circle, increase until it looks right, then continue with a tube until it looks right, then continue making a U-shape until it looks right, then fold the slipper in half and sew up the back.
And to Rorichan: I can always use new slippers! (Size 11, hint hint, nudge nudge, wink wink)