Preheat the oven to 200C/400F/Gas 6. Grease a 12-hole muffin pan well, then set aside.
Whisk together the flour, sugar, baking powder, baking soda, salt, and spices. Set aside.
Whisk together the egg, buttermilk, oil, and vanilla extract. Pour the wet ingredients into the dry ingredients, and mix until just combined. Do not over-mix. (The batter will be VERY thick and somewhat lumpy.) Gently fold in the apple chunks.
For the Streusel
In a small bowl, whisk together the flour, sugar, and cinnamon. Add the melted butter, and mix until evenly distributed and the mixture is crumbly.
Spoon the batter into the prepared pan, top with the streusel, and bake for 15 - 20 minutes, or until a toothpick inserted into the centre comes out clean. Allow to cool for 5 - 10 minutes in the pan before transferring them to a wire rack to cool completely.
Video
Notes
*To make your own buttermilk, simply measure out 1 cup (240ml) of milk, and stir in 1 tablespoon of lemon juice or white vinegar. Let stand for 5 - 10 minutes until the mixture starts to curdle, then it's ready to use!Muffins stay fresh in an air-tight container at room temperature for up to 5 days. They also freeze well for up to 2 months. Thaw overnight in the fridge.