Fill a small or medium saucepan with water and bring to a boil. (Do not add salt.) Peel the potato. Cut it into quarters, then into approximately ½ inch pieces. Once the water comes to a boil, add the potato pieces, cooking for 10-12 minutes, just until they are tender enough for a fork to easily slide into them. Drain, mash and allow to cool a bit until lukewarm. Weigh out 110 grams or measure out ½ cup. (Save the rest for dinner.)
Place all of the dough ingredients except for the salt into the bowl of an electric mixer. (Or knead them all by hand in a bowl.) Knead on a medium speed until a dough forms, approximately 2-3 minutes. Lower the speed and slowly add in the salt. Increase the speed to medium and continue kneading until the dough passes the windowpane test.
Shape the dough into a ball and cover with plastic wrap. Allow it to double in size, approximately 1 hour and 45 minutes.
In a small bowl, mix the sugar, cinnamon and flour together. Set aside.
Spray a 9-inch by 5-inch loaf pan with non-stick spray.
Punch down the dough and give it a few kneads by hand. Roll it out into a long rectangle, approximately 6 inches by 20 inches. Brush a thin layer of oat milk all over the dough, except for the top ½ inch. Sprinkle with the cinnamon mixture and then the raisins. Use the rolling pin to gently push the filling and raisins into the dough. Roll the dough up and pinch the seams together. Place the dough into the prepared pan. Cover loosely with plastic wrap and allow to rise for one hour.
Approximately 30 minutes into the second rise, preheat the oven to 350° F.
At the end of the second rise, the dough should have risen approximately 1 inch above the top of the pan. Bake for 45 minutes. The internal temperature of the dough should be at least 190° F. Immediately remove from pan and allow to cool completely on a wire rack.