Once fully cooled, keep muffins in an airtight container at room temperature for up to 2 days or refrigerate for 3–5 days. Freeze cooled muffins in a zip-top bag with excess air removed for up to 3 months; thaw overnight in the fridge, in short microwave bursts, or at room temperature. Fresh or frozen berries may be used—if using frozen, expect a firmer batter. For dairy-free preparation, substitute non-dairy milk for the yogurt and use neutral oil instead of butter. To make these gluten-free, replace the flours with a gluten-free cup-for-cup blend. For an egg-free version, omit the eggs, add ½ cup milk, and increase baking soda to 1 teaspoon. For mini muffins, use a 24-cup mini muffin tin and bake for 12–14 minutes.