Preheat the oven to 200°C/180°C fan/gas mark 6.
Place the sweet potatoes into a saucepan, cover with water and boil for 10 minutes.
Drain excess water, set aside and allow to cool.
Add 40g of the butter and white and red onions to a saucepan and cook over a medium heat for 5 minutes or until soft.
In a casserole dish, layer the vegetables; half the onions, third of Violife, half the potatoes, followed by the remaining onions, another third of Violife, the remaining potatoes and finally top with the remaining Violife.
Season to taste and bake in the oven for 1 hour and 30 minutes or until golden and cooked through.
This recipe has been specifically designed for a low protein diet. Refer to labels for allergen and other product information.