So here is my step by step - hopefully it's helpful, even though Sweet P's is a great tutorial for potholders. :)
Materials to make a 4"x4" coaster:
- three coordinating fabrics
- small square of batting or fusible fleece
- Cut two squares 4.5"x4.5" of each of three fabrics. Sandwich a square of batting between your bottom and "window" fabrics (base). Fold the other four squares in half to form triangles and press.
- Lay one triangle on the base with the two raw sides lined up with raw edges of the base. Overlap the second triangle, then the other two in turn, around the base. You will tuck the last triangle under the first one.
- Pin each edge and corner in place, being sure to have all raw edges even.
- Sew around the square with 1/4" seam allowance, then clip the corners.
- Turn the coaster right side out through the centre and push out the corners.
- Fold the edge of each triangle back on itself to show the base fabric in a little window. Pin them down.
- Topstitch on the folded edges. You can either topstitch both edges of each fold, or only the inner one.