Ch 2 at beg of row does not count as hdc.
Ch 44 (47).
1st row: (WS). Sl st in 2nd ch from hook. 1 sc in each of next 4 ch. 1 hdc in each of last 38 (41) ch. Turn. 43 (46) sts.
2nd row: Ch 2. *Work 1 hdc in single horizontal bar created between sts of previous row (bar is below loops normally worked). Rep from * 37 (40) times more. Working in back loops only, 1 sc in each of next 4 sc. Sl st in last sl st. Turn.
3rd row: Ch 1. Sl st in first sl st. Working in back loops only, 1 sc in each of next 4 sc. *Work 1 hdc in single horizontal bar created between sts of previous row. Rep from * 37 (40) times more. Turn.
Rep 2nd and 3rd rows for pat until work across long edge (when slightly stretched) measures approx 18½ (20)" [47 (51) cm] ending on a 2nd row of pat. Fasten off leaving a long end to sew back seam.
Sew back seam.
Crown shaping: 1st rnd: (RS). Join yarn with sl st at crown edge of back seam. Ch 1. Work 30 (34) sc evenly around top edge of Hat. Join with sl st to first sc.
2nd rnd: Ch 1. *Draw up a loop in each of next 2 sc. Yoh and draw through all 3 loops on hook – sc2tog made. Rep from * around. Join with sl st to first st. Fasten off, leaving a long end. Draw end tightly through rem 15 (17) sts.
Pom-pom (optional): Wind yarn around 4 fingers approx 80 times. Remove from fingers and tie tightly in center. Cut through each side of loops. Trim to a smooth round shape. Sew pom-pom to top of Hat.