Use 4 ply wool and you will need three colours
You will also need toy stuffing

Base
Using first colour cast on 8 stitches
Row 1 Purl
Row 2 K2 (YFON, K1) 5 times, K1 (13 stitches)
Row 3 Purl
Row 4 K2 (YFON, K1) 10 times, K1 (23 stitches)
Row 5 Purl
Row 6 K2, (YFON, K1) 20 times, K1 (43 stitches)
Row 7 Purl
Row 8 Knit
Row 9 Cast off in Purl leaving a long end of the wool
Using the end, with right sides together, sew the two sides of the circle together, and put to one side as it is now time to make the actual cupcake.
Cupcake
Continuing with the first colour cast on 44 stitches
Row 1 [wrong side] P2, (K1, P1) repeat to the end of the row
Row 2 (K1, P1) repeat until the last 2 stitches, K2
Repeat these rows 2 more times which means you now have 6 rows
Row 7 P2, (K1, P1), repeat to the end of the row
Row 8 K1, P1 (YFON, K1, P1) 20 times, YFON K2 (65 stitches)
Row 9 P2 (K into the made loop, K1, P1) and repeat
Row 10 (K1, P2) until last 2 stitches, then K2
Row 11 P2 (K2, P1) to the end
Row 12 (K1, P2) repeat until the last 2 stitches and then K2
Row 13 Cast off loosely following the ribbing
Now you need to select your second colour and pick up 45 stitches at the back of the cupcake. You need to have the right side facing and I normally pick up the stitches from the 2nd row down. Make sure the stiches are even across the whole width of the cupcake.
Row 1 Purl
Row 2 Knit
Row 3 Change to your third colour and Purl a row
Row 4 Purl
Row 5 Knit
Row 6 Purl
Row 7 Knit
Row 8 Purl
Row 9 Knit
Row 10 P2, (P2 together, P1) 4 times [31 stitches)
Row 11 Knit
Row 12 (P1, P2 together) 10 times, P1 (21 stitches)
Row 13 Knit
Row 14 P1, (P2 together) 9 times, P2 (12 stitches)
Row 15 Knit
Cut the wool leaving a long tail for sewing up.
Making sure the two right sides are together, sew up the seam using the right colour thread for each part of the cupcake.
Using a new piece of wool in the first colour, attach the circular base to the cupcake and just sew round ¾ of the way. Then stuff the cupcake and finish sewing up.
Decorate as you wish.