Adapted from 50 Heirloom Buttons to Make by Nancy Nehring (Taunton Press 1995, now out of print)
Cut four 1 1/2" (3.8-cm) and six 1⁄2" (1.3-cm) circles out of cardboard. Cut a 6-yard (5.5-m) length of yarn and thread it on a tapestry needle. Beginning at center of wrong side of form, wrap yarn around cardboard circle from top to bottom two times, then again from side to side two times (Step 1).
Turn form over and rotate it 45 degrees so that previous wraps form an X. Working from top to bottom, wrap yarn around form from side to side 10 times for large buttons (Step 2) and 8 times for small buttons, covering the cardboard between diagonal lines of X.
Working right to left, wrap yarn 10 times for large buttons and 8 times for small buttons around form from top to bottom, using needle to weave yarn over upper half of horizontal threads and under remaining threads a total of 5 times for large buttons and 4 times for small buttons, then under top group of threads and over bottom group an equal number of times (Step 3).
End by fastening off yarn on back of button.
I got this from the Knit Daily newsletter