First make the pastry: mix the flour, instant oat cereal, oil and mustard and a pinch of salt with enough cold water to bring the mix together into a wet dough which comes away cleanly from the sides of your mixing bowl. The dough should be easily manipulated and stretchy, but not stick to your fingers.
110 ml vegetable oil, 225 g self-raising flour, 2 tsp mustard powder, 35 g oat
Leave to rest for half an hour at room temperature.
Filling
Meanwhile, prep the filling. Heat the oil and sugar on your hob in an oven and hob-proof dish. (Flan dish, large flat bottomed pyrex lasagne dish, etc)
2 tbsp vegetable oil, 1 tbsp sugar
Slice the onions. Arrange beautiful slices on the base of your oven-proof dish and cook for around 10 minutes. Then add the balsamic and oregano. Put the oven on at Gas Mark 4 or 180C.
500 g onion, 2 tbsp balsamic vinegar, 2 tsp oregano
Keep an eye on the pan and cook for another 10 mins, they should go a lovely brown colour but will burn easily. When they are reduced down, gently press down to form an even layer.
Place your pastry crust on top (doesn’t matter if it doesn’t cover the whole thing or has holes in as the upside-down nature of it means it will still cook!)
Bake for 35-40 mins, until golden brown Turn out onto a plate. This will give 4 generous portions. The balsamic adds a little extra tartness that is very tasty!