Apple & blackberry crumble cake

Ingredients

• For the cake
• 280g plain flour
• ½ tsp ground cinnamon
• ¼ tsp salt
• ½ tsp baking powder
• 1 ¼ tsp bicarbonate of soda
• 120ml olive oil
• 160g golden caster sugar
• ½ a vanilla pod
• 2 eggs, lightly beaten
• 2 bramley apples, sliced skin on
• 150g blackberries
• Grated zest of a lemon
• 2 egg whites
• For the crumble:
• 100g plain flour
• 50g butter, melted
• 50g dark brown sugar