I did this block for coasters once. I used a square of say 5.5" for the background, and then I cut four squares (two in two colors) of say 3.5", folded them on the diagonal, and then pinned them with raw edges to the edge of the big square. I stitched around the edge of the big square, securing all the edges, and then turned inside out.
Obviously, this made them thick, but that was the point of a coaster. The background square peeked through.
I'm thinking this block is from the Farmer's Wife quilt block series…maybe if someone has it, she could look it up...