This is the knitting pattern for a mug cosy, worked in rib and twist stitch pattern. It has a stocking stitch area for a motif - in this case I have used a heart for your valentine, but you could embroider any thing you like. The heart is embroidered on using the swiss darning technique.
The pattern instructions are given for a shaped mug as in the photo, and for a straight sided mug.

Materials
Approx half (36 metres) of a 50g ball of of DK (light worsted) colour Grey
2 metres of contrast for Heart
2 matching buttons
1 pr no 4 mm needles (UK/Canada/Australia no.8/US6)
Wool sewing needle and a large eyed normal sewing needle

Tension
Over stocking stitch on no 4 mm needles (UK/Canada/Australia no.8/US6) - 20 sts and 26 rows = 10 cm square. Use larger or smaller needles if necessary to obtain correct tension.

Thanks for looking!