Place squares in opposite corners, lining up the outer edges. Sew diagonally from corner to opposite corner on each square.
Press the square over on itself toward the corner. Make sure your edges are even.
You may trim out the back of the square only or trim both pieces (and use them for tiny pinwheels!!). Just be sure the fabric on top lines up with the edges of the large square before you do or it will be harder to match your patches as you piece.