Peel and chunk the potatoes. Put in a large pot and cover with water. Add two tablespoons salt and bring to a boil.

Cook until potatoes are soft, about 15 to 20 minutes. Drain potatoes and return pot to the stove over low heat. Cook until potatoes are dry. Transfer to a large bowl of mixer fitted with the whisk attachment.

Melt butter in a medium frying pan. Add onion and sauté until lightly golden. Remove from heat and add onions to potatoes. Mix on low speed to break up potatoes.

Add milk and cheese; beat on high until mixture is smooth and fluffy. Season with salt and pepper. Cover and refrigerate until very cold.

Scoop 1/3 cup of batter and roll into a three-inch log. Dredge in flour, dip in eggs and coat with panko. Set aside on a tray and chill until cold.

Fill a deep sauté pan with at least two inches of oil. Heat oil to 350 degrees Fahrenheit on a deep fry thermometer. Add croquettes and fry until golden on all sides and cooked through. Remove with slotted spoon and drain on a cooling rack.

Serve warm with spicy mayo for dipping.