200 g unsalted butter
440 g (2 cups) sugar
1 tsp vanilla extract
250 g (1 cup) sour cream
250 ml (1 cup) Mushroom cream (see below)
300 g (2 cups) plain (all-purpose) flour
90 g (1 cup) chestnut flour
2 tsp baking powder
1 tsp bicarbonate of soda (baking soda)
1 tsp salt
Figs, to serve
The Mushroom Cream:
10 g dried porcini mushrooms
625 ml (2 1/2 cups) thick (double/heavy) cream
The Porcini Caramel:
110 g (1/2 cup) sugar
2 Tbs light corn syrup
60 ml (1/4 cup) water
185 ml (3/4 cup)
Mushroom cream (see above)
To make the mushroom cream, add the porcini mushrooms and cream to a saucepan and bring to a gentle, frothy boil. Reduce the heat to low and simmer for 10 minutes, until slightly reduced and deeply fragrant.
Strain into a container, pressing down gently on the porcini with a fork to extract the last of the liquid. Discard the porcini.
For the porcini caramel, carefully stir the sugar, corn syrup and water together in a small, high-sided saucepan set over a medium–high heat. Using a sugar thermometer to check, bring the mixture to a temperature of 180°C (350°F), then remove from the heat and leave to rest for 1 minute. Using a metal whisk, slowly stir 185 ml (6 fl oz/¾ cup) of the mushroom cream into the hot syrup mixture (the remainder will be used in the cake so don’t throw it away or drink it) for 2–3 minutes until the caramel settles. Set aside.
Preheat the oven to 180°C (350°F). Lightly grease and line a 22 cm (9 in) square cake tin with baking paper.
Beat the butter, sugar and vanilla together in a large bowl for 10 minutes until creamy. Add the eggs one at a time, followed by the sour cream and 250 ml (8½ fl oz/1 cup) of the mushroom cream. Fold in the flours and the other dry ingredients and mix together gently to combine.
Spoon the batter into the prepared tin and bake for 1 hour, or until a skewer inserted into the centre comes out clean.
Remove the cake from the oven and leave to cool slightly in the tin for 5 minutes, then carefully turn out onto a wire rack. While still warm, smother the cake in the porcini caramel and leave to set before serving.