To make the mashed sweet potato, take two medium-large sweet potatoes and prick them a couple of times with a sharp knife. Microwave for around 10 minutes, turning them over halfway through, until they are soft. Alternatively, you can bake them at 180C/350F/gas mark 4 for around 40 minutes. I DO NOT recommend boiling or steaming them however as it will make the cake too wet.
Allow to cool a little then peel off the skin, place the flesh in a bowl and mash. Measure out 230g/1 cup of the mash for the bread and reserve any left over for another use.
Preheat the oven to 180C/350F/gas mark 4. Grease an approx 22x11cm/8.5x4.5in loaf tin and line with a strip of baking parchment.
To make the streusel, mix the flour, sugar and cinnamon together in a bowl. Add the margarine and rub in using your fingertips until no lumps of fat remain and the mixture resembles crumbs. Stir in the chopped pecans and place in the fridge.
To make the sweet potato bread, whisk together the flour, baking powder, bicarbonate of soda, spices and salt.
In a separate bowl, whisk together the mashed sweet potato, sunflower oil, almond milk, cider vinegar, caster sugar and light brown soft sugar.
Tip in the dry ingredients and fold through until well combined but be careful not to over-mix. The batter should be quite thick.
Scrape the batter into the prepared tin and spread it level. Scatter over the streusel topping evenly and press it down very gently.
Bake for 60-80 minutes, until a skewer inserted into the centre comes out clean. Cover loosely with tin foil part way through baking if the top starts to colour too much.
Leave to cool in the tin for 10 minutes then carefully lift out of the tin using the strip of baking parchment and place on a wire rack to cool completely. Store in an airtight container for up to 5 days.
For the best results make sure that you follow the recipe closely. As always, I highly recommend using the gram measurements (with a digital scale), rather than the cup conversions. Cup measurements are simply not accurate enough for baking and I cannot guarantee the best results if you use them.