Cook the potatoes in lightly salted boiling water until tender. Leave to cool and then put through a ricer to make a fine texture.
Heat the butter in a skillet and lightly fry the garlic with mustard. Add the cream and heat just until warm. Stir into potatoes to make a smooth mashed potato.
Stir in the blue cheese, 500 grams of the panko crumbs and spinach.
Portion the mixture into golf-sized balls. Chill for easier handling if you need to.
Toss the balls in the flour, then dip in the egg. Roll in the panko. Then deep fry.