1. Preheat your oven to 375°F or 190°C.

2. In a large mixing bowl, whisk together 225g or 2 1/4 cups of flour, 200g or 1 cup of sugar, and 6g or 1 1/2 teaspoons of baking powder.

3. In a separate bowl, whisk together 240ml or 1 cup of milk, 1 egg, and 55g or 1/4 cup of melted butter.

4. Combine the wet and dry ingredients until smooth.

5. Gently fold in 225g or 1 1/2 cups of frozen blueberries.

6. Divide the batter evenly among 14 muffin cups.

7. Bake for 20-25 minutes or until a toothpick comes out clean.

8. Meanwhile, prepare the oat crunch topping by mixing 60g or 1/2 cup of rolled oats, 50g or 1/4 cup of brown sugar, and 1.25g or 1/4 teaspoon of salt in a small bowl.

9. Cut in 55g or 1/4 cup of cold unsalted butter until crumbly.

10. Sprinkle the oat mixture over the muffins before baking.

11. Once the muffins are done, allow them to cool completely.

12. Dust with powdered sugar and garnish with a sprinkle of ground cardamom if desired.