At least a couple of hours or up to a couple of days ahead, roast and puree the pumpkin. Preheat your oven to 200⁰C/400⁰F (combination steam setting). If your oven has variable steam settings, use 80% (if not, don’t worry! Just set to combi steam at the correct temperature and the oven will take care of the humidity).
Put the pumpkin into a solid baking tray and roast it for about 20 minutes, or until very soft and starting to brown on the edges. Let it cool slightly, then scrape the flesh off the skin (discard the skin), and puree in a food processor or blender. Set aside until cool. You’ll need 1 ½ cups in total, if you have a little leftover you can freeze it for next time or use it for something else (I quite like leftovers stirred through hot pasta with ricotta, peas and bacon for a quick dinner).
When you're almost ready to make the cake, brown your butter. Put the butter in a pan over medium-high heat. Let it melt, then cook, stirring or swirling the pan frequently, until the milk solids start to turn a medium golden brown colour (this takes 5-7 minutes for me but will depend on how hot your pan is). When it’s done, your kitchen will start to smell like buttery roasted nuts. Tip it out of the hot pan into a heatproof bowl quick smart, or it’ll keep cooking. Black butter is not good for much. Let it cool while you get the rest of the ingredients ready.
Set your oven to 180⁰C/350⁰F (combination steam setting). If your oven has variable steam settings, use 60%. Line a 12-hole regular sized muffin pan with paper or foil cases. You’ll turn out and re-use the pan later to make the remaining cakes.
In a large bowl, mix the flour, baking soda, spices and salt together, then make a well in the centre.
Measure 170g (6 oz) of your browned butter into a mixing jug or bowl (stir it up just before you measure it out as the solids will have sunk during cooling). Set the rest of the butter aside for the frosting. Add the cooled pumpkin, sugars, eggs and milk and whisk well to combine. Pour this mixture into the flour and stir to mix everything together.
Divide your batter into the cases (if, like me, you’re pedantic about these things, you could set your tray atop your scales and put exactly 70g into each case. Or just be a normal person and guess it). Bake until the cakes are risen, golden and spring back when pressed with a fingertip, around 12 minutes. Remove from the oven, let them sit in the tin for a couple of minutes, turn out and repeat the process with the remaining batter. Let the cakes cool completely before frosting.