- With the rack in the middle position, preheat the oven to 350°F (180°C). Butter a 9 x 5-inch (23 x 13 cm), 6-cup (1.5 litre) loaf pan. Line with a strip of parchment paper, letting it hang over two sides.
- In a bowl, whisk together the oil and brown sugar. Add the eggs one at a time until smooth. Add the sour cream, orange zest and juice. Mix until combined. Add the flour, baking powder, baking soda and salt.
- Spread half of the batter out in the prepared pan. Top with half of the plums, lightly pressing them into the batter. Cover with the remaining batter and remaining plums, cut side down. Lightly sprinkle the top of the cake with brown sugar.
- Bake for 1 hour or until a toothpick inserted in the centre of the cake comes out clean. Let cool completely on a wire rack. Unmould and slice.
When in season, use 4 to 6 small plums, such as Mount Royal plums.