Bring 1 inch of water to a boil over high heat in a vegetable steamer or a large saucepan fitted with a portable vegetable steamer. Peel one potato and cut into eighths; steam the pieces until tender when pierced with a fork, about 15 minutes. Rice or mash pieces in a large bowl; set aside to cool for 15 minutes. Position the rack in the center of the oven; preheat the oven to 375∞F. Lightly oil a large baking sheet with canola oil dabbed on a paper towel. Peel the other potato and grate it through the large holes of a box grater. Squeeze of any excess moisture; add to the riced or mashed potatoes. Stir in the egg, egg white, oil, milk, chives, and caraway seeds until fairly smooth. Add 3 1/4 cups flour, baking powder, and salt; stir with a wooden spoon until the mixture forms a soft but sticky dough. Lightly flour a clean work surface as well as your cleaned and dried hands. Turn the dough out onto the floured surface and knead for 1 minute, adding flour in 1-tablespoon increments to keep the dough from turning too sticky. Too much flour and the dough turns tough; it should remain a little tacky but workable. Shape into an 8-inch circle, flatten slightly keeping the loaf mounded at its center, and place on the prepared baking sheet. Use a sharp knife to slash an X in the top of the dough, cutting into dough about 1/2 inch. Bake until golden brown, firm to the touch, and somewhat hollow sounding when tapped, about 55 minutes. Cool 1 hour on a wire rack before slicing and serving. Makes 1 large loaf (16 slices).