Peel and dice the Russet Potato into ½"-1" dice. Add 2 cups of water and the diced potatoes to the inner pot of the Ninja Foodi. Put the pressure lid on and turn the valve to seal. PC on high for 2 minutes. Immediately release the pressure. Drain the potatoes and mash with a fork, make sure to get all lumps mashed up. Set aside to cool.
In a medium size mixing bowl, combine 3 cups of flour, salt, baking powder, and the mashed potatoes. Mix. The mixture will be a little lumpy, but try to get the lumps about pea size.
Make a well and add in a lightly beaten egg. Add the oil and the milk. Stir to combine. The dough will start out wet and tacky and you will usually need to add an additional ¼-¾ cup of flour. Add ¼ cup at a time. When a shaggy dough ball forms, put it on a floured surface. Preheat the Ninja Foodi on bake/roast @375°F for 5-10 minutes.
Knead the dough just until it comes together. Add more flour if it is too tacky. Form a log and place it in the loaf pan. Gently press it down so it covers the bottom of the pan and is even on top. Make deep slits in the bread about 2" deep with a sharp knife or scissors.
Place the pan on the rack in the low position and place into the inner pot of the Foodi. Select Bake/Roast at 325°F and bake covered (foil or silicone cover) for 30 minutes. Remove the cover and continue to bake on 325°F for another 20 minutes.
Brush some butter on top and close the TenderCrisp lid. Let the bread sit in the Ninja Foodi for another 20 minutes. This will finish cooking the middle. Remove and cool. You can either flip the bread out onto a cooling rack or cool in the pan.
Slice & Serve