1. Cook the potatoes in lightly salted boiling water until tender. Leave to cool and then put through a potato ricer to make a fine texture.
2. Heat the butter in a skillet and lightly fry the garlic with the mustard. Add the cream and heat just until warm. Stir into potatoes to make a smooth mashed potato.
3. Stir in the blue cheese, spinach, and about 1/8 of the panko crumbs.
4. Portion the mixture into golf-sized balls. Chill for easier handling if you need to.
5. Toss the balls in the flour, then dip in the egg. Roll in the rest of the panko. Then deep fry.
6. Season with salt and serve warm.