In a separate bowl, mix together the baking soda and vinegar. Then add this to the flour. Knead a soft dough from these ingredients.
Leave the resulting dough aside, covered with a towel, to rest for about 20 min. Afterward, shape the dough into a round loaf.
Set aside a little of the dough for decorating the loaf. Prepare suitable Christmas decorations from it. Smear with oil on top. Bake in a preheated 392°F (200 °C) oven for about 40 min.