In a large bowl, mix potatoes, melted butter, egg, soda, salt, and ½ cup flour. Mix until soft and lump-free, and a dough forms, do not overwork. Keep adding more flour to dough until dough is firm and holds a shape and is not sticky to the touch - but not so much flour it crumbles apart. This will depend a lot on your potatoes, humidity in the air, etc - so you will have to add more flour and go based off feel instead of giving a precise measurement. 

Sprinkle a little flour out on a table and add dough to table. Work into large circle and shape into a disc. You will have enough for two to three discs - depending on how thick you'd like them. I like them thick so they are a bit like mashed potatoes in the middle still, but it's more traditional to make them thinner.

Cut disc into four wedges. 

Heat a nonstick frying pan or well seasoned cast iron skillet on the stove over medium high heat. 

When the pan is hot, add dough wedges to pan. 

Let bread cook and brown on each side, about 5 minutes per side. Rotate bread and flip onto each side, so it is browned on all edges. I prefer a darker browning for a bit of crunch, but a light toasting is traditional - how browned you like your bread is up to you. Use a wooden spoon to help flip bread. 

When bread has browned on all sides, it is done. 

Serve hot with butter, sour cream, or jam, depending on if you made it savory or sweet.