Preheat your oven to 160°C / 140°Fan /Gas 3 /325°F with a shelf in the middle position.

Butter and/or line a 2lb/900 ml capacity non-stick loaf tin.

Make the topping

Put all the ingredients for the topping EXCEPT the butter in a small bowl and stir together.

Add the butter and use your fingertips to rub it into the other ingredients until you have a sandy, crumbly mixture. Set aside.

Make the cake batter

Sift together the flour, chai spice mix and salt. Set aside.

Put the sugar, butter, and vanilla extract into a large bowl and, preferably using electric beaters, beat until soft and light. Scrape down the bowl as necessary during this and subsequent steps.

Beat in the eggs one at time along with 1 tbsp of the flour mixture each time.

Beat in half the yogurt plus 1 tbsp of the flour, followed by the remaining yogurt and another tablespoon of flour.

Fold in the rest of the flour plus the walnuts.

Transfer the batter to the prepared tin, smooth the top, then sprinkle over the topping.

Bake and cool the cake

Put into the preheated oven and bake until an inserted skewer or cocktail stick comes out clean: approximately 60 - 75 minutes.

Tip: check at 55 minutes to see how it's going as over-baking can result in a dry cake.

Put the tin on a cooling rack for 10 minutes then take the cake out and leave on the rack until completely cold before decorating and/or slicing.

Make the icing and decorate the cake

Sift together the icing sugar and chai spice mix.

Add 1 tbsp of the milk or water plus the vanilla extract. Use a small whisk to combine, adding more liquid a drop at a time until you have a pouring consistency: you may not need to add all the liquid.

Whisk in a small pinch of salt if liked.

Drizzle the icing over the top of the cake, allowing it to run down the sides.

Sprinkle with the finely chopped walnuts and small pinches of chai spice.

Serving and storing

Serve cut into slices. To serve warm, lightly reheat in a microwave.

Best eaten within 3 days or can be frozen.