Melt the butter in a pan

Mix in everything, stirring well

Preheat the oven to 150°C

Pour out the mixture onto a big baking tray lined with baking paper

Pat down the jacks with a wooden spoon or something

Leave them in the oven for 45 minutes, probably 30 minutes for fan ovens

Take them out carefully and let them cool a bit

Use a knife to cut them into portions

Best kept in the fridge, they will keep good for 3 days