Method

1. Heat the oven to 220C/200C fan/gas 7. Cut the squash in half, scoop out the seeds, then put both halves cut-side down on a baking tray lined with baking parchment. Roast for 30 mins until a sharp knife easily pierces the flesh. Leave to cool completely. Put the cooled squash halves in a high-powered blender (no need to peel) and blitz to a smooth purée. Reduce the oven temperature to 180C/160C fan/gas 4.

2. While the squash cools, make the praline for the topping. Put the pecans on a small baking tray lined with baking parchment and roast in the oven until lightly toasted, about 5-6 mins. Melt the sugar in a medium saucepan over a low heat, gently swirling the pan until all the sugar has melted fully. Turn the heat up, swirling the pan every now and then until you have a deep amber caramel. Carefully pour the caramel over the nuts, and leave to cool completely (it will harden as it cools).

3. Butter a 20cm deep cake tin and line with baking parchment. Put the butter, both sugars and the spices in a large bowl and beat using an electric whisk until light and fluffy, about 4-5 mins. Whisk the eggs, soured cream and olive oil together in a small jug, then pour this into the butter mixture, a little at a time, whisking between each addition. Pour in the butternut squash purée and fold to combine (don’t worry if it splits a little), then fold in the flour, bicarb and a pinch of salt. Pour the batter into the tin and bake for 1 hr at 180C/160C fan/gas 4, or until a skewer inserted into the middle comes out clean. Leave to cool in the tin for 20 mins, then remove to a wire rack and leave to cool completely.

4. Break the cooled praline into shards. Set some aside for decorating later, then tip the rest into a mini chopper or food processor and blitz to fine crumbs. For the buttercream, put the butter and soured cream in a stand mixer and beat until light and airy. Add the crushed praline and icing sugar and whisk on low to just combine, then turn the speed up to medium, whisking for a few minutes until you have a fluffy buttercream.

5. Slice the cake in half through the middle. Put one cake half on a cake board or plate, then spread over half the buttercream, smoothing it to the edge (or, pipe mounds over the cake using a piping bag fitted with a round nozzle to cover). Sandwich the second cake half on top, then spread or pipe over the remaining buttercream. Roughly chop the reserved praline shards, then scatter these over the top. Will keep chilled for up to four days. Bring to room temperature before serving.