Plum Crumble

Name: Plum Crumble
Prep time: 15 min
Cook time: 30 min
Total time: 45 min
Cuisine: American
Ingredients: 2.5 lb ripe purple plums (stoned and halved - 1.15 kg); 1/2 cup white granulated sugar (100g); 1 teaspoon finely grated lemon zest (unwaxed organic); 2 tablespoons cornstarch; 1 cup all-purpose/plain flour (125g); 1/3 cup ground almonds (30g); 1/3 cup soft light brown sugar (67g ); 1/2 teaspoon sea salt; 1 teaspoon baking powder; 1 teaspoon ground cinnamon; 1 teaspoon vanilla extract; 6 tablespoons cold unsalted butter, cut into cubes (90g ); ice cream or clotted cream (to serve)