This is a very easy stand alone single knot stitch. It looks like a knot in the centre of a cross. The legs of the cross can be made short or long, depending on how you want the effect to be. This stitch can be used as a stand alone stitch or can be used in multiples as a filling stitch.

four_legged_knot_stitch_1      four legged knot stitch 2
Fig 1: As shown, Bring the needle out from A, in through B and out through C. The point C is in right angle to A and B.   Fig 2: Now, take the needle under A-B without plucking the fabric beneath. Twist the thread from C under the needle as shown. When you would pull out the needle, you would get a knot over A-B.
four_legged_knot_stitch_3   Fig 3: To finish off, take the needle in through a point right angled to A and B, and in straight line to C.
You get a knot with four legs. The length of the legs can be adjusted by adjusting the distance of stitch between A, B and C.