Preheat oven to 375°F. Spray a 12-muffin pan with coconut oil cooking spray.
In a large bowl, whisk flours, baking soda, baking powder and salt. In a medium bowl, mix bananas, brown sugar, egg, butter, milk and vanilla extract. Add wet ingredients to dry ingredients and mix until just combined.
Make crumble: In a medium bowl, combine flour, brown sugar, pistachios, cardamom and salt. Using your fingers, knead butter into dry ingredients until mixture resembles wet sand.
Fill each muffin tin about ⅔ of the way and top with crumble. Bake at 375°F until crumble is golden brown and a toothpick comes out clean, 18-20 minutes. Let cool and serve. Muffins will keep in an airtight container for up to 5 days.
