Cook potatoes in boiling, salted water to cover 15 minutes or until tender. Drain, cool, and peel potatoes; chop coarsely.
Combine potato, garlic, 1/4 cup green onions, salt, and pepper; set aside.
Rub 3 (6-inch) cast-iron skillets with olive oil. Bake at 450° for 10 minutes.
Add 1 tablespoon butter, coating bottom of 1 skillet. Spoon one-third potato mixture into hot skillet, pressing lightly with back of spoon. Dot with 1 tablespoon butter, and sprinkle with 1 tablespoon green onions. Repeat procedure with remaining skillets.
Cook on top of range over medium-high heat 5 minutes or until golden on bottom. Bake at 450° for 5 minutes or until golden on top. Cut each cake in half.
Note: Recipe may be prepared in 1 (12-inch) cast-iron skillet. Turn out, and cut in wedges.