- Slip one stitch knitwise.
- Slip a second stitch knitwise.
- Slip both stitches back from right to left needle.
- Knit both stitches together through the back loops.
Alternative faster method (shown in video):
After slipping both stitches to the right needle, when you insert the left needle into the front of both stitches, instead of slipping them back you can immediately knit them together through the back loop to save time.
See this in action in the video here: