Preheat the oven to 180C/356F. Grease and line a 22 X 12cm loaf pan.
Combine the dry ingredients (sugar included) in a mixing bowl and whisk until combined.
Add the wet ingredients and whisk until a smooth orange batter forms. The batter should be about the consistency of a thick but flowing yoghurt.
Add the chocolate, if you’re using it, and then decant the batter into the lined loaf pan.
Top with the crumble, if you are using it. You can also use some finishing sugar or leave the loaf pan.
Place into the oven and bake for 30 minutes or until a skewer comes out clean and the loaf is firm without any wobble. Allow to cool for 10 minutes before transferring to a wire rack.
Keeps for a number of days in an airtight container.
To make the (optional) crumble topping:
Combine all ingredients in a small bowl. Massage together until a crumb forms.
Notes
If you're using fresh nutmeg or grating your own, use less than recipe specifies.
You can also use pumpkin spice if you have it. I have never tried it, but I would recommend starting at 2 teaspoons.
I make my own pumpkin puree from Japanese or Kent pumpkin. See the body of the post for my method (it's important!)
Personally, I find the best way to enjoy this pumpkin cake is with a sprinkle of sugar as the topping, rather than the streusel. I wanted to include the option, but I find the streusel makes the cake beneath taste less sweet and less spiced than it is.