Blueberry Crumble with Yogurt

Ingredients

• 2 cups (11 oz or 300 g) fresh blueberries
• 1/4 cup (2 oz or 60 g) blueberry preserves
• 1 cup (4 oz or 125 g) yellow cake mix
• 1/2 stick (2 oz or 60 g) butter, cut into small cubes
• low-fat vanilla yogurt, to serve