8 large eggs, lightly beaten with a little seasoning
100g firm goat's cheese, broken into chunks
Heat oven to 190C/170C fan/gas 5. Heat the oil in a 25cm ovenproof frying pan. Add the onions and cook for 10-15 mins until soft and caramelised. Add the kale and 1 tbsp water, and cook for 5 mins until the kale has wilted. Pour in the balsamic vinegar and bubble for 1 min, then add the eggs. Give everything a quick stir, then leave undisturbed to cook over a low-medium heat for 5 mins until the egg is nearly set and the frittata is turning golden brown on the bottom.
Scatter the goat’s cheese over the top of the frittata. Cook in the oven for 10-15 mins until the cheese is bubbling and the frittata is set in the centre.