I watch Fons and Porter's Love of Quilting every week. I've even got Mom watching it every so often. I'd seen the epiosde where they made these coasters. And then a few days later Mom asked if I'd seen the show as she'd like a set of them.
Start with four pieces of 5"coordinating fabrics. Fold them in half diagonally wrong sides together and press. The 5th one is the back.
Lay two triangles on the backing piece.
Put the 3rd piece (the blue one) over half of one piece from the step above and under half the other piece.
Then put the 4th piece (the cream one) under and over opposite from the 3rd piece.
You should end up with half of each triangle showing.
Pin or clip the pieces together and sew around the edges. I didn't get a picture of the next step. Open up the coaster in the hole in the center where the four fabrics meet and turn it inside out. This hides the seams.
Topstitch around the edges, and you're finished. The coaster in this picture is the same one as the one above that but because I turned it inside out, the fabrics are opposite.