These classic muffins with a streusel topping are satisfying plain or packed with berry mix-ins (as long as they do not exceed 1 1/4 cups). Good additions include blueberries, raspberries, strawberries, or peaches.
Preheat oven to 400 degrees. Butter a standard muffin tin. Combine flour, baking powder, cinnamon, and salt in a large bowl; whisk to combine.
In a medium bowl, combine butter, vanilla bean scrapings, sugar, milk, and egg; whisk to combine. Fold butter mixture and fruit into flour mixture; use no more than 10 strokes.
Spoon 1/4 cup batter into each prepared cup; press 2 tablespoons streusel on top of each. Bake until tops are golden, 15 to 17 minutes. Remove from oven; let cool in pan 15 to 20 minutes before transferring to a wire rack. Serve warm or at room temperature
For best results, bring milk, eggs, and butter to room temperature. Take these ingredients out of the refrigerator before you start, letting them warm up as you measure the dry ingredients.