Fill a medium saucepan with a 2cm depth of water. Cut the sweet potato into roughly 5cm chunks and add them to the saucepan then place over a medium heat on the hob. Once the water begins to boil, place a lid onto the saucepan and turn the heat down to low. Allow to steam for 15-20 minutes or until the sweet potato is tender and easily pierced with a fork. Drain the steamed sweet potato and blend in a food processor or blender into a smooth puree. Set aside.

Preheat the oven to 200°C/180°C fan/Gas mark 4. Grease each cup of a 12 Cup Le Creuset Muffin Tray with a bit of vegetable oil using a pastry brush.

In a medium bowl, mix the melted butter, yoghurt, eggs, sugar and cinnamon. Mix until smooth then weigh out 300g of the sweet potato puree and stir in. Next, add the flour, baking powder, bicarbonate of soda and salt. Stir gently until just combined. Finally fold in the chopped dark chocolate and pecans.

Divide the batter evenly between the cups of the muffin tray (the batter should come close to the top of the cups). Bake for 20-25 minutes until well-risen and a toothpick inserted into the centre of a cupcake comes out clean. Allow to cool for 10 minutes in the tin before removing to a wire rack to cool completely.

Fill a medium saucepan with a 5cm depth of water and place over a medium-low heat on the hob. Set a large, heatproof bowl over the saucepan. Add the egg whites and sugar to the large bowl and stir constantly until the sugar has dissolved (the mixture shouldn’t feel gritty when stirred) and registers 70°C on a thermometer.

Remove the bowl from the pan and use electric beaters to whisk the mixture until cool, very fluffy and thickened - you should be able to lift up the beaters and form stiff peaks in the mixture which do not sink back into the meringue.

Use a palette knife to cover the top of each cooled cupcake with a swirl of the meringue. If you have a kitchen blowtorch, use it to gently toast the meringue. Keep in an airtight container for up to 3 days.