This technique is a simple Brioche decrease, that decreases 3 stitches into one. It has a right leaning effect, which makes it the opposite to the traditional ssk (slip, slip, knit) stitch.
To work a Brioche ssk, or brssk, follow these instructions. I have broken them down by one individual action per line, as Brioche stitches can sometimes look overwhelming, when you first look at them.
slip 2 stitches individually knitwise (including the yarn over)
insert left needle into the stitches and knit together through the back loop
transfer the resulting stitch to the left needle
lift the next stitch on the left needle over this stitch
drop the lifted stitch off the needle
transfer stitch back to the right needle to continue with the next instruction.