Heat oven to 200C/fan 180C/gas 6. Arrange the mushrooms on a baking tray. Scatter over the cheese, walnuts, thyme sprigs and butter. You can do up to this stage a day in advance.

Pop in the oven and cook for 10 mins until the cheese is melted and the mushrooms are softened. Arrange some rocket leaves on plates and place the mushrooms on top.

Whisk the mash and the egg into the lukewarm syrupy mixture, then stir everything into the dry ingredients. Pour the batter into the prepared tin, scatter with most of the crystallised ginger and bake for 45 mins until a skewer poked into the centre comes out with just moist crumbs attached. Scatter over the remaining sliced ginger to stick, then cool in the tin. This cake tastes delicious once thoroughly cooled and sliced, but even better if wrapped in parchment and foil, and left for a couple of days to mature. Perfect with a cuppa, smeared with some butter.