This pattern is made with 3 individual pieces:

1. Back of Cover (BC)
2. Front of Cover Bottom (FCB)
3. Front of Cover Top (FCT)

BC - Rows 1 to 25
Cast on 35 + ch 3 for first dc
dc first 2 rows with colour A, hdc third row with colour B,
repeat until you have 17 rows in colour A and 8 rows in colour B

Row 26:
sl st 12, ch 3, dc 11, sl st 12, cast off

Rows 27 and 28:
start at first dc of row 18. ch 3, dc 11

Rows 29 to 32:
ch 3, in first ch 1 dc, 11 dc, in last ch 1 dc, cast off end row 24

FCB - Rows 1 to 20
Cast on 35 + ch 3 for first dc
dc first 2 rows with colour A, hdc third row with colour B,
repeat until you have 14 rows in colour A and 6 rows in colour B, cast off.

FCT - Rows 1 to 10
Cast on 35 + ch 3 for first dc
dc first 2 rows with colour A, hdc third row with colour B,
repeat until you have 7 rows in colour A and 3 rows in colour B

Row 11:
sl st 12, ch 3, dc 11, sl st 12, cast off

Rows 12 and 13:
start at first dc of row 18. ch 3, dc 11

Rows 14 to 17:
ch 3, in first ch 1 dc, 11 dc, in last ch 1 dc, cast off end row 17

Add a "button" row at the bottom of row 1 (yellow in the picture)
ch 2 in first ch, hdc 10, ch 3, skip 3, hdc 11, ch3, skip 3, hdc 10, cast off.

Matching it up:
Place FCB and FCT on BC the wrong way round and sl st all the way round the pieces like in the picture on your left. Make sure that all coloured lines are matching up (you may have to cheat a bit).

When you are done, turn the cosy inside out with the right way up and add a trim to the top (red in the picture)

Trim:
ch 2 in any dc, hdc all the way round, cast off.

Sew on some buttons and you have yourself a super soft cosy :)