The original! The SOFI method (squares on fusible interfacing) makes child's play of assembling watercolor quilts.
Place squares aligned on the grid (fusible side up), fuse in place, then take the entire project to the sewing machine as one piece, not two-by-two!
Fold and stitch horizontal seams.
Snip intersections, then fold and stitch vertical seams. If you are using Bonny Tinling's book Watercolor:
An Easy Approach (item#: 95207), order:
2 yards for Tablerunner
3 for 35 inch Square Wallhanging
4 for 35x50 inch Rectangle Wallhanging
6 for Baby; 8 for Lap
14 for Twin; 20 for Double/Queen
24 for King.