Turned satin stitch
This is a variation of satin stitch: rather than the stitches remaining parallel across the design area, they are angled so that the stitch direction follows the shape of the design.
For more information see the entry for satin stitch.
Outline the shape with split stitch and fill with any padding required (satin stitch or split stitch). Bring the needle up just outside the split stitch outline partway along the shape. Choose the required angle and take the needle down accordingly, just outside the split stitch.
Bring the needle up on the first side again, very close to the first stitch, just outside the split stitch. Make a second stitch, angling the needle towards the previous stitch and towards the split stitch.
Continue to stitch in this way to cover the shape. To change the angle gradually as you move along the shape, bring the needle up even closer to the previous stitch on the inside curve and take it down a little further away on the outside curve.
Complete the first half of the shape with a last neat stitch. Try to think about the angles in advance so that when you get to this stitch, it will easily cover the outline.
Begin again in the middle. As for the basic satin stitch, you will reverse the direction of the stitches.
This time, to change the angle, bring the needle up a little further away from the previous stitch on the outside curve and tuck it even closer on the inside curve.
Structure of stitch
Various Authors, The Royal School of Needlework Book of Embroidery (2018) , p.330