Plum Crumble Cake

Name: Plum Crumble Cake
Prep time: 25 min
Cook time: 45 min
Total time: 1 h 10 min
Cuisine: British
Ingredients: 150 g plain flour (all-purpose) (BL55); 30 g cornflour (cornstarch) (cornstarch); 100 g light brown sugar; 1 tsp baking powder; 1 tsp pure vanilla extract or 1/2 tsp of vanilla paste; 75 ml neutral-tasting oil (coconut, vegetable or sunflower oil); 150 ml non-dairy milk (almond, oat, rice or soy milk) (room temperature); 1 pinch fine sea salt; 500 g fresh plums; 30 g light brown sugar (2 tbsp); 1/2 tsp ground cinnamon; 100 g plain flour (all-purpose); 50 tsp light brown sugar; 50 ml coconut oil