Preheat your oven to 400F (200C). Line a 6-cup muffin tin with paper liners.
To make the crumb topping: add the flour, sugars, salt, and cinnamon to a deep bowl; whisk to combine. Using a fork, stir in the melted butter, making sure there are no dry bits of flour; set aside.
To make the muffin batter: add the flour, sugar, salt, and baking powder to a clean deep bowl. In a small bowl or large measuring cup, combine the buttermilk, egg, and melted butter. Beat with a fork.
Pour the buttermilk mixture over the flour mixture. Stir with a fork until just combined. Using a rubber spatula, fold in the berries.
Evenly spoon into the prepared muffin tin. Tap the pan lightly on the counter so the batter settles into the cups. Evenly sprinkle the crumb topping onto the muffins, pressing it in gently so it sticks.
Bake until a deep golden brown, 25 to 30 minutes. Remove from the oven. Set the tray on a wire rack, and allow muffins to cool at least 10 minutes before serving.