Heat a medium sized saucepan and add a good splash of olive oil (about 2 tbsp). Add onions and saute until soft (about 15 mins). Add sugar and vinegar and cook for a further 15 minutes. Season well. Whisk together eggs cream water and season with salt and pepper. Spray a 12 hole muffin pan with oil and cut pastry into 12 squares. Press each square into a muffin hole and add a tsp caramelised onion and a tsp crumbled feta. Pour over egg mixture and bake for 10-15 minutes until golden and cooked through.