Preheat oven to 425 degrees F. Spray a 12 count muffin tin with cooking spray or line with liners. Set aside.
Combine dry ingredients (flour, baking powder, baking soda, salt, cinnamon, cardamom) in a medium bowl. Mix to combine and set aside.
In a separate large bowl add cooled brown butter and brown sugar. Whisk to combine.
Add egg, greek yogurt, mashed banana and vanilla to bowl with browned butter and brown sugar. Whisk to combine.
Add dry ingredients to bowl of wet ingredients in three batches. Gently mix with a rubber spatula. Be careful not to overmix.
Using a large cookie scoop or spoon, fill muffin tins flush to the top with batter. Top muffins with 2 tbsp. of streusel and gently press into top of muffin.
Bake muffins in a 425 degree F oven for 5 minutes. Then lower heat to 350 degrees F and cook muffins for an additional 10-15 minutes. Check muffins with a toothpick to check for doneness. If the toothpick comes out clean the muffins are done. Let muffins cool in tins for 5 minutes and then remove from tins and let cool on a cooling rack.
Muffins stay fresh covered at room temperature for 2 days, then stored covered in the fridge for up to 1 week.