To make the left slipper: Using size 10 (6 mm) needles and main color, cast on 61 sts. Sole Row 1 (RS): K61. Row 2: K1, M1, k59, M1, k1. (63 sts) Row 3: Knit. Row 4: K1, M1, k61, M1, k1. (65 sts) Work 8 rows in garter st (knit every row). Upper Row 1 (RS): K26, place marker (pm), k13, pm, k26. Rows 2, 4, and 6: Purl, slipping markers when reached. Row 3: K24, ssk, slip marker (sm), k2tog, k9, ssk, sm, k2tog, k24. (61 sts) Row 5: K23, ssk, sm, k2tog, k5, ssk, sm, k2tog, k23. (57 sts) Row 7: K22, ssk, sm, k2tog, k1, ssk, sm, k2tog, k22. (53 sts) Row 8: Knit. M1 increase Ssk decrease K2tog decrease Garter stitch seam Mattress stitch seam Whip stitch Row 9 (RS): K10, bind off next 33 sts, k to end (10 sts now on needle after bind-off).**
Strap Row 1 (WS): K10, cast on 15 sts onto right needle, slip remaining 10 sts onto a stitch holder. (25 sts) Turn and cont on these 25 sts only. Row 2: K25. Row 3 (buttonhole): K23, yo, ssk. Row 4: K25. Bind off all 25 sts. Return to sts on stitch holder and with WS facing, rejoin main color and knit all 10 sts from stitch holder. Work 3 rows in garter stitch (knit every row). Bind off.
To make the RIGHT SLIPPER Work as for Left Slipper to **. Next row (WS): K10, slip remaining 10 sts onto a stitch holder. Turn and cont on these 10 sts only. Work 3 rows in garter stitch (knit every row). Bind off.
Strap Row 1 (WS): Using size 10 (6 mm) needles and main color, cast on 15 sts onto right needle, then with same needle and WS facing, knit all 10 sts from stitch holder. (25 sts) Row 2: K25. Row 3 (buttonhole): K2tog, yo, k23. Row 4: K25. Bind off all 25 sts.
To Sew the Seams: Fold the finished slipper piece in half lengthwise with right sides together, and sew the cast-on edges together with a simple whip stitch. Turn the slipper right side out so the right side is facing you and use a garter stitch seam to sew the garter stitch sole of the heel. Insert the needle into the top loop of the stitch on one side and then in the bottom loop of the corresponding stitch on the other side (1 and 2). Continue alternating from side to side. When you reach the upper (St st) area of the slipper, switch to mattress stitch to complete the heel seam. Insert the needle under the horizontal bar between the first and second stitches and then under the bar on the corresponding stitch on the other side (3 and 4). Continue alternating from side to side. To Finish: Sew a small button onto the outside edge of each slipper to correspond with the buttonhole. If desired, use size 6 (4 mm) needles and contrasting double-knitting weight yarn to make two 3-stitch i-cords 11" long for bows. Tie in bows and sew one to the front of each slipper. Weave in any stray yarn ends.
This pattern is excerpted with permission from <a href="http://amzn.to/1SQ1Rlj">"Hooked on Knitting: 20 Fresh and Funky Hand-Knit Designs (Simple Makes)"</a> by Jessica Biscoe (Barron's).