Preheat oven to 350oF (180oC).
Line a loaf pan (4.5 x 8.5 inch ; 11 x 22 cm) with parchment paper. Set aside.
To a bowl, add sugar and water. Whisk until sugar is completely dissolved.
Then add oil and vanilla extract and mix well.
Sift in flour, baking powder and baking soda.
Mix until dry flour is no longer visible. DO NOT OVER MIX (mix until dry and wet ingredients are just combined).
Add blueberries and gently fold into batter.
Transfer batter into loaf pan. Spread batter evenly.Add blueberries and rock sugar on top. Bake in preheated oven to 350oF (180oC), rack middle position, 40-45 minutes, or until toothpick inserted in the middle of cake comes out clean.
Let loaf cool down in pan for 10 minutes. Then transfer to wire rack to cool down completely.