Recipe: Spiced Sweet Potato Cake with Marshmallow Frosting

I'll make pretty much anything to use up what's lurking around in the cupboard or fridge. I hate to waste food. Usually this involves some form of dinner which, in my family, is known as an 'around the world dinner'. By this, you can expect any combination of leftovers of all sorts of cuisines.

I couldn't quite face eating a bag full of sweet potatoes to myself this week so set out to find a suitable use for them. After making a few pumpkin cakes with cans of Libby's last year I was keen to try sweet potato and see how they compare.

This sweet potato cake is slightly more dense than the pumpkin ones I made last year and has much more flavour. But, if you do have a can of Libby's pumpkin purée hanging around, you can substitute with the same quantity.

Spiced sweet potato cake with marshmallow frosting
(Recipe slightly adapted from Smitten Kitchen)

680g sweet potatoes (approximately 2-3)
115g unsalted butter, room temperature
190g soft light brown sugar
2 large eggs
1/2 tsp vanilla extract
250g plain flour
1 3/4 tsp baking powder
1/2 bicarbonate of soda
1/2 tsp salt
1 tsp ground cinnamon
1/4 tsp ground ginger
1/4 tsp ground cloves, or mixed spice

Marshmallow frosting:

3 large egg whites
180g golden caster sugar
pinch pf salt
1/4 tsp cream of tartar
1/2 tsp vanilla extract

Prick the sweet potatoes all over and roast in the oven at 180 degrees for 30 - 45 minutes. They may need a turning a few times. Once cooked they'll be soft and look a little deflated. Leave to cool completely. If you're baking in advance, leave them in the fridge for up to 3 days, otherwise give them plenty of time to cool before moving onto the cake.

Heat the oven to 170 degrees and grease and line an 8 - 9 inch round springform tin, or an 8 - 9 inch square tin.

Peel the sweet potatoes and mash until smooth (don't be tempted to blitz in the blender, your mix will be too loose).

Cream together the butter and sugar until light and fluffy. Gradually add the eggs in one at a time, mixing well after each addition. Add the vanilla extract.

Gently fold in the sweet potato, followed by all the dry ingredients. Continue until well incorporated. Pour the batter into the prepared cake tin, smooth the top with a knife and bake for 35 - 40 minutes. Once baked, a skewer inserted into the middle should come out clean. Leave to cool for 10 minutes in the tin before turning out to cool completely on a wire cooling rack.

To make the frosting, add the egg whites, sugar, salt and cream of tartar to a heatproof bowl and place over a pan of barely simmering water. Whisk for approximately 3 minutes, until the sugar has fully dissolved. Remove the bowl from the saucepan and continue to whisk with an electric mixer for a further 4 - 7 minutes on a high speed, until stiff, glossy peaks form. Add the vanilla and mix to combine.

To decorate, spread a thin layer of the marshmallow onto the cake with a palette knife or spatula. Then, with a piping bag or sandwich bag, pipe small dollops over the thin frosting layer. With a kitchen torch, lightly brown the marshmallow dollops until browned.

Find my recipe for sweet potato brownies here if you'd like to try them another way.

Alternatively, you could substitute the same quantity of pumpkin for sweet potato in my spiced pumpkin mini cakes or in my pumpkin praline cake.