Follow these steps carefully to ensure your muffins turn out perfectly moist, flavorful, and tall every single time. The key is to combine the ingredients correctly and, most importantly, not to overmix the batter.

1. Preparation and Preheat: First things first, prepare your oven and muffin tin. Preheat your oven to 400°F (200°C). This initial high heat helps the muffins rise quickly, creating those desirable domed tops. Line a standard 12-cup muffin tin with paper liners or grease it generously with butter or non-stick spray. Setting this up first ensures your batter can be baked immediately once it’s mixed.
2. Combine the Dry Ingredients: In a medium-sized mixing bowl, add the whole wheat flour, baking soda, baking powder, salt, and ground cinnamon. Use a whisk to stir everything together for at least 30 seconds. This step is more important than it seems; it thoroughly distributes the leavening agents (baking soda and powder) and salt, which guarantees that every muffin will rise evenly and be perfectly seasoned.
3. Mash Bananas and Mix Wet Ingredients: In a separate, larger mixing bowl, peel your very ripe bananas and add them to the bowl. Using a fork or a potato masher, mash them until they are mostly smooth. A few small lumps are perfectly fine and will add pockets of banana flavor to the finished muffins. To the mashed bananas, add the packed brown sugar, the room-temperature egg, the melted butter (or coconut oil), and the vanilla extract. Whisk these wet ingredients together until they are just combined and the egg is fully incorporated.
4. Combine Wet and Dry: Pour the dry ingredient mixture from the first bowl into the large bowl containing the wet ingredients. Using a rubber spatula or a wooden spoon, gently fold the ingredients together. Be very careful here: do not overmix. Mix only until the flour streaks have just disappeared. The batter will be thick and lumpy—this is exactly what you want. Overmixing develops the gluten in the whole wheat flour, which will result in tough, dry, and dense muffins instead of tender ones.
5. Fold in the Nuts: Add your chopped walnuts or pecans to the batter. Gently fold them in with just a few strokes, distributing them evenly without overworking the batter. If you’re adding any other mix-ins like chocolate chips, do it at this stage.
6. Fill the Muffin Tin: Using a large spoon or an ice cream scoop for uniform size, divide the batter evenly among the 12 prepared muffin cups. Each cup should be filled about two-thirds to three-quarters of the way full. This gives the muffins enough space to rise without overflowing. For a professional bakery-style look, you can sprinkle a few extra chopped nuts and a pinch of brown sugar on top of each muffin before baking.
7. Bake to Perfection: Place the muffin tin in the preheated 400°F (200°C) oven and bake for 5 minutes. Then, without opening the oven door, reduce the oven temperature to 350°F (175°C). Continue to bake for another 13-15 minutes. The total baking time will be around 18-20 minutes. The muffins are done when they are golden brown on top and a wooden skewer or toothpick inserted into the center of a muffin comes out clean or with a few moist crumbs attached (but no wet batter).
8. Cooling Process: Once baked, remove the muffin tin from the oven and let it cool on a countertop for about 5 minutes. This allows the muffins to set slightly, making them easier to remove. After 5 minutes, carefully transfer the muffins from the tin to a wire cooling rack to cool completely. Allowing them to cool on a wire rack prevents the bottoms from becoming soggy as steam escapes.