Use bananas with brown spots and soft flesh for maximum sweetness and moisture; overly ripe bananas (almost black) provide the best flavor and natural binding without extra sugar.

Bring eggs, sour cream, and butter to room temperature before mixing to ensure even distribution and a lighter, fluffier crumb structure in your muffins.

Mix wet and dry ingredients until just combined to avoid developing gluten, which makes muffins tough and dense; a few lumps are perfectly fine and desirable.

Make your cinnamon-brown sugar streusel with cold butter cut into small pieces, then sprinkle it on batter right before baking so it creates a crispy, distinct topping rather than sinking into the cake.

Fill each cup two-thirds full with batter, then add a spoonful of streusel, then top with remaining batter to distribute the topping evenly throughout the muffin for better texture in every bite.