For the cake:

Butter 50g

Sugar 70g

Egg 1

Milk 60g

Flour 140g

Baking powder 1 tsp

Salt 1/4 tsp

Blueberry 1 small box ( because I only had 1 small box, which is around 120g. You can add more if you like rich blueberry flavor)

1. Mix flour, baking soda, and salt in a large bowl.

2. In another bowl, cream butter and sugar till creamy.

3. Beat in egg and vanilla.

4. Add in flour mixture and milk alternately till flour mixs in. Stir in blueberries.

Pour the batter into pan.

For the top:

Brown sugar 50g

Flour 3 tsp

Cinnamon powder 1 tsp

Butter 2 tsp

Combine all the topping ingredients in a small bowl (except butter). Cut in butter. And make them into crumb. Sprinkle over batter.
Preheat oven to 180 degree C. Bake for around 45 mins. Or when it can pass the toothpick test.

It is very similar to the blueberry cake I baked before:
https://chewbaccascook.wordpress.com/2016/09/24/blueberry-cake/