I wasn't in the mood for inset seams at 6 'o clock last night, so I devised another plan. If you're allergic to reverse applique you may want to use a different method.
Print or trace the block diagram onto freezer paper. Cut out the center diamond neatly. Cut it into three sections and number them as shown in the photo.
Using your favorite foundation piecing technique, foundation piece the three sections and attach them to form the center diamond. Leave a generous seam allowance around the outer edges of the diamond. Mine was at least half an inch. This is important for the next step.
Cut a 6" square out of your foundation fabric. Cut it in half twice on the diagonal and reassemble it as we did in block A-3.
Using a hot, dry iron, iron the freezer paper square onto the fabric square, making sure to center it by lining up the diagonal lines of the pattern with the diagonal seams of the square.
Cut the center diamond out of the fabric, leaving a ¼" seam allowance. Clip the seams almost to the freezer paper edge.
Place the pieced diamond face up on the table. Place the fabric square face up on top of it, centering the diamond carefully.
Baste all around through all the layers, making sure to leave room around the edge for turning the seam under when you applique. This is why leaving a lot of fabric around the edge of the diamond was important.
Using reverse applique like we have in previous blocks like C-9, attach the diamond to the fabric square. Remove the freezer paper and press.
Use your favorite needle turn applique method to applique a diamond to each end of the pieced diamond as in the picture. I used the "freezer paper inside" method as in block E-1. If you're using this method, remember to remove the freezer paper from the inside of the diamonds when you're done. Just open up the seam at the back of the diamond and pull out the freezer paper.
Press the block and trim it to 5".
Mine is actually quite straight. It looks skew in the photo because of the angle I photographed it at.