Preheat the oven to 350 degrees F. Line a muffin pan with paper liners and set aside.: The moment you preheat, the kitchen begins to fill with a warm promise of baked aroma, and the oven reaches a stable environment that ensures even rising. You want an oven that reads true to temperature, so if yours runs cool or hot, adjust accordingly, because an incorrect temperature can cause dense centers or overly browned tops. Lining the pan with paper liners creates a barrier that makes removal effortless and keeps edges soft rather than crisp, which suits these muffins. If you skip liners, lightly grease the pan to prevent sticking, and note that the muffins may brown more on the sides.
In a medium bowl, whisk together flour, baking powder, baking soda, salt, and cinnamon. Set aside.: As you whisk, you will notice the dry mixture turn uniform in color and texture, which signals even distribution of leaveners and spice. This step ensures lift is consistent in each muffin and prevents pockets of salty or soapy tasting leavener. A common mistake is to skip this and add dry ingredients straight into the wet, which can yield uneven rise. Once combined, set the bowl aside so the dry ingredients are ready to be folded in quickly, preserving the air in the batter.
Peel the bananas and mash with a fork. Place the mashed bananas in a large bowl. Add the brown sugar, coconut oil, almond milk, and vanilla extract. Stir until well combined. Slowly stir in the dry ingredients. Mix until just combined. Carefully fold in the blueberries.: Right away you will smell the warm, molasses like notes of the brown sugar mixing with banana perfume as you mash. The texture should be lumpy, not completely puréed, which keeps the muffins tender. When you add melted coconut oil and room temperature almond milk , the batter becomes glossy and silky; stirring until just combined preserves air for lift. Overmixing will make the muffins tough, so stop when no dry streaks remain. Folding in the blueberries gently prevents bursting and discoloring the batter, while still distributing fruity pockets throughout. If you fold too aggressively, you risk turning the batter purple and deflating it.
Fill muffin liners three-quarters full. Sprinkle with turbinado sugar, if desired. Bake until toothpick inserted into center comes out clean, about 25 minutes. Transfer to wire rack to cool. Store, covered, at room temperature.: Filling the liners to three quarters provides room for a domed top without spilling over; you will see the batter rise and form a golden crown. Sprinkling with turbinado adds a satisfying crackle and sparkle on top when baked. As they bake, the kitchen will be scented with cinnamon and sweet banana aromas, and you should see gentle browning at the edges and slightly domed tops. A toothpick should come out clean or with a few moist crumbs, not wet batter. Removing them to a wire rack prevents steam from condensing under the muffins which keeps the bottoms from getting soggy. Cooling partially before eating ensures the crumb sets properly. If you leave them in the pan too long, the residual heat can overcook them.
Note - these muffins freeze well. To reheat, place muffin in the microwave for about 30 seconds.: When frozen, the muffins maintain texture and flavor remarkably well, and reheating briefly softens them back to a freshly baked state; the brief microwave pulse revives moisture and aroma. Wrap individually or store in a sealed container to avoid freezer burn, and allow them to thaw slightly before microwaving to heat evenly. Avoid overheating as it can make the muffins gummy. If reheating from thawed, use shorter times to prevent drying out.