Preheat the oven to 350°F (175°C). Line a standard 12-cup muffin tin with paper liners or coat with nonstick spray.
Mix the dry ingredients
In a medium bowl, whisk together the flour, baking powder, baking soda, nutmeg, cinnamon, cardamom, and salt. Set aside.
Cream butter and sugar
In the bowl of a stand mixer, beat the softened butter and brown sugar together until smooth and creamy.
Incorporate eggs and vanilla
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract until fully incorporated.
Combine dry ingredients and yogurt
Add one-third of the dry ingredients to the butter mixture, followed by one-third of the yogurt. Mix well after each addition. Repeat this process until all dry ingredients and yogurt are incorporated.
Fold in bananas and walnuts
Using a spatula, gently fold in the diced bananas and chopped walnuts until evenly distributed throughout the batter.
Fill and bake
Divide the batter evenly among the muffin cups. Bake for 25–30 minutes, or until the tops are golden brown and a toothpick inserted into the center comes out clean.
Cool and serve
Allow the muffins to cool in the pan for 5 minutes before transferring them to a wire rack. Serve warm or at room temperature.
Notes
To prepare this recipe gluten free, substitute the all-purpose flour with a certified gluten-free flour blend in equal measure. Ensure that baking powder and other ingredients used are labeled gluten free to prevent cross-contamination.