Combine the starter and water in a medium bowl until well mixed. Add sugar, oil, whole wheat flour, all-purpose flour, and salt, then stir until the dough forms.

Cover with a damp towel and let it rest for 1 hour. Perform a “stretch and fold” technique to strengthen the dough: pull the dough’s edges toward the center, working around the bowl for about a minute until it forms a smooth ball.

Cover again and let rest at room temperature for 8-12 hours, allowing the dough to rise and develop flavor.

Grease an 8x3-inch loaf pan. Turn the dough onto a floured surface, press it into a 9x12-inch rectangle, and sprinkle evenly with cinnamon and sugar. Roll from the shorter (9-inch) edge, tucking in the ends, and place in the loaf pan.

Cover and allow the loaf to rise for 1-3 hours or until it reaches about ½ inch above the pan’s rim.

Preheat the oven to 375°F (190°C) and bake for 40-45 minutes, until golden brown. Let the loaf rest in the pan for 5 minutes, then transfer to a wire rack to cool for at least 1 hour.