Heat oven to 375 degrees F. With some of the oil, lightly grease a shallow ovenproof dish, big enough to accommodate the potatoes in a single layer. Peel the potatoes, wash them, and dry them. They all should be the same size, approximately 3-½x2 inches. Shape them to this size, if necessary.
Slice each potato 4 times, widthwise. Between each slice, put a piece each of bacon and sage. Spread onion slices in the bottom of the pan. On top put the potatoes, one next to the other, tightly together so they won’t fall apart. Pour half of the warm bouillon over all. Grease top of potatoes with some oil and sprinkle pepper over them. Salt may be used, but sparingly, since the bacon is already salty. Bake 50 to 75 minutes. If bouillon evaporates, add some more. When the potatoes are done, they are tender inside, crusty on the outside, and no bouillon is left in the pan.
Let rest for 3 to 4 minutes before serving along with the onions.