Blackberry Muffins with Cardamom Crunch Topping

Name: Blackberry Muffins with Cardamom Crunch Topping
Prep time: 10 min
Cook time: 30 min
Total time: 30 min
Yield: 12 pieces
Ingredients: 30 g plain flour; 30 g light brown sugar; 25 g unsalted butter; ½ tsp ground cardamom; 120 g granulated sugar; 1 lemon; 100 g unsalted butter; 100 g plain yoghurt; 180 g plain flour; 2 large eggs; 2 tsp baking powder; 250 g fresh blackberries