Yield: This recipe makes 16 standard-size muffins.
Technique: Stir the batter only until you no longer see dry streaks after each flour and milk addition. Overmixing once the flour goes in overdevelops the gluten and is the primary reason muffins turn out dense.
Measuring: For the crumble topping, the butter must be cold when you cut it in. Softened or melted butter will clump instead of forming the coarse, sandy texture you want.
Storage: Store cooled muffins in an airtight container at room temperature for up to 2 days. To freeze, place in a single layer on a baking sheet first, then transfer to a zip-top bag and freeze for up to 2 months. Reheat frozen muffins in a 325ºF oven for about 10 minutes, or in the microwave for 30 to 45 seconds.