Insert your hook into the top of any stitch, starting with one chain, then working a double crochet into each stitch. At the corner-spaces, work one stitch into the corner-space, then work a dc2tog across the two corner-spaces.
STEP 1 Insert your hook into the corner-space, yarn over and pull up a loop.
STEP 2 Insert your hook into the next corner-space and pull up a loop. Yarn over again and pull through all loops on your hook.
STEP 3 Like with the edging on your squares, do (dc, ch, dc) into each corner. Finish up each round with an invisible finish.
STEP 4 Work a few rounds in different colours to finish off.