In Jane's Field of Dreams block the corners of the square do not quite reach the sides of the block, where in the book they do.
Here's what I did:
Cut 1 square 3 1/2" from the center fabric (white, in this case). Cut 2 squares 3 1/2" from the triangle fabric. Cut each of the second squares in half diagonally.
Sew a triangle to each of two opposite sides of the square. The diagonal edges of the triangles will be longer than the edge of the square. Make sure to center the triangles along the edges of the square.
Press open and trim off the little bits overhanging the edges.
Now attach the remaining two triangles to the square. Remember to center them along the edge of the square again.
Press, trim, and we have a lovely block D-13: Field of Dreams!