Dusting blueberries with flour prevents them from sinking during baking., Properly shredding and pressing zucchini removes excess moisture and ensures soft, fluffy muffins without soggy bottoms., Filling muffin cups three-quarters full helps avoid batter overflow and mess., Using oil instead of butter is an option, especially to avoid dairy; applesauce or mashed bananas can be used but may make muffins denser., Fresh blueberries are preferred, but frozen blueberries can be used if thawed and drained., Muffin batter can be baked in loaf pans; baking time increases to about 1 hour., The streusel topping is optional; it adds crunch and sweetness but increases calories and fat., Store cooled muffins in airtight container at room temperature for up to 2 days, or refrigerated for 4–5 days., Freeze individually wrapped muffins for up to 3 months; thaw overnight in fridge or 1–2 hours at room temperature., Reheat refrigerated or thawed muffins in microwave for 15–30 seconds or oven at 325°F for 8–10 minutes., Make-ahead tip: prepare batter night before, refrigerate covered up to 24 hours; gently stir before baking.