Melt 25g of the chocolate in a bowl over a pan of hot water. Add the marshmallows and stir until melted then add the butter. Stir well. Add the rice crispies to the chocolate and marshmallows and stir to coat evenly. Allow to cool slightly then form into eight cones shapes. Flatten the large end to make a wide brim. Allow to cool and stiffen. Melt the remaining chocolate. Dip the cones into the chocolate and coat evenly. Place on waxed paper or tinfoil to cool and harden.