Walnut & Coffee Cake with Streusel Topping

For the walnut cake:
90g walnut halves
3 tbsp sunflower oil
215g unsalted butter, softened
175g light soft brown sugar
1½ tbsp golden syrup
3 eggs
220g white spelt flour
2 tsp baking powder
¼ tsp sea salt

For the coffee icing:
175g unsalted butter, softened
250g icing sugar, sifted1 tsp vanilla extract
1 espresso shot, or 3 tbsp strong coffee
¼ tsp sea salt

For the streusel topping:
55g spelt porridge flakes
55g unsalted butter, melted and cooled
55g demerara sugar

Preheat the oven to 160°C/315°F/Gas 2-3.

Put the walnuts in a roasting tin and roast for 12-14 minutes until they are light brown. Remove from the oven and leave to cool, then tip into a blender, add the oil and blitz to a dry walnut paste.

Turn the oven temperature up to 170°C/325°F/Gas 3 and line two 20cm/8in round cake tins and a baking sheet with baking paper.

Beat together the butter and sugar in a large bowl, using an electric mixer, until pale and fluffy. Add the syrup, then the eggs, one at a time, followed by the roasted walnut paste. Mix the flour, baking powder and salt in a small bowl, then fold into the mixture. Divide the cake mixture equally between the prepared cake tins.

Bake for 30 minutes, or until the top looks golden brown and feels firm to the touch. If in doubt, a skewer inserted in the centre should come out clean. Transfer to a wire rack to cool.

While the cakes are cooling, turn the oven up to 180°C/350°F/Gas 4 and scatter the topping ingredients over the prepared baking sheet. Bake for 15 minutes, or until is crisp and golden brown in colour. Remove from the oven and allow to cool before using on the top of the cake.

To make the filling and icing, beat the butter in a large bowl, using an electric mixer, until soft, then gradually add the icing sugar and beat until pale and fluffy. Add the vanilla, espresso and salt and whisk again until fluffy. Spread about one-third of the creamed mixture on top of the first sponge cake, then place the second sponge on top. Spread the remaining mix over the top and around the side of the assembled cake and scatter the toasted streusel mixture on top to serve.