Cut two 5 inch x 5 inch squares from your flannel fabric and one 5 inch x 5 inch square from the batting.
Place the flannel fabric together with print sides facing towards each other, the batting on top and pin together.
Sew a 1/4 inch around leaving one side open to be able to flip right side out.
Turn the raw edges in on the unsewn edge and sew 1/4 inch all around the coaster for a finished look.
Finished!