Start with a cone, not cup shaped ice-cream cone and a sharp, serrated knife (I used a steak knife)

Carefully cut the tip and some of the top so that you are left with the middle section. Cut it as high as you would like your hat to stand. If you want a bigger, wider hat, just cut the pointed tip and not the open end. This should give you a bigger hat.

Roll out and cut a strip of fondant as wide as the hat is tall. Attach it to the cone piece using a small amount of water or tylose glue. trim and secure a seam making the back of the hat.

I folded the top edge over rather than trimming it off. This provided a nice edge to secure the top piece at the end.

Add a band from a rolled ribbon of fondant. Attach again with water or tylose glue.

I added a big buckle. You could use a mini heart-shaped cutter to create a shamrock or decorate however you like.

Roll out more green fondant and cut with a circle cutter to get the brim of the hat in a diameter you’re happy with. try to keep it in proportion. Attach the covered cone to the brim with water or tylose glue and fill with mini m&m’s

Cut a smaller diameter circle from the green fondant that is the right size for the top of the hat and attach to seal in the chocolates.