This took quite a bit longer than expected.
I apologize for the quality of the photos. The light was very strange today.
So here's what I did:
Print or trace the block diagram onto freezer paper and cut out all the shapes that will be in the main block fabric. Cut carefully so that your piece of freezer paper doesn't fall apart. Keep the bottom scalloped section to use later.
Iron the freezer paper pattern onto the right side of a piece of background fabric large enough to cut down to the block size with seam allowances later.
Cut the bottom scalloped section out of the fabric, leaving a seam allowance for turning under when appliqueing. Clip the curves.
Cut a piece of main block fabric the same size or a little larger than the background fabric.
Lay this on the table right side up. Lay the background fabric section on top. Baste through all the layers around the edges of the block to stop fabric shifting.
Baste along the scalloped edge, leaving enough room between the basting and the edge to turn under the seam.
Applique along the scalloped edge, turning under the seam allowance as you go.
Cut the large diamond out of only the background fabric, being careful not to cut the main fabric layer. Leave a seam allowance all around (about 1/8" to 1/4").
Baste along the edge to secure the fabric layers, leaving enough room to turn under the seam allowance when you applique.
Applique the large diamond by turning under the seam allowance as you go and clipping the sharp corners.
Use the same technique to reverse applique the small bottom diamonds.
Applique the small top diamond in the same way.
Iron the scalloped section of freezer paper you saved back in position on the block to help you trim the block accurately.
Trim around the block, leaving 1/4" seam allowance. Also cut off the little top diagonal section 1/4" above the seam line.
Cut a small piece of background fabric with at least one straight edge. Line this up with the top diagonal edge of the block and sew the 1/4" seam. Press open. Trim the top of the block back into shape. This was easier for me than trying to make a teenie little pattern for the top section.
Remove the freezer paper and basting.
(I mirrored my diagram because I thought I was going to foundation piece the top so it's the wrong way round. There's NO way I'm redoing it.)