I often make these delicious little tartlets for my vintage tea parties. They look pretty, they’re full of flavour and are dainty enough to be served alongside finger sandwiches. Cooked slowly with a little brown sugar and some balsamic vinegar, the red onions take on a lovely caramelised flavour as they soften. I usually make these as a gluten free option, swapping the plain flour for some Doves Farm gluten free plain white flour. I find that it is best to leave this pastry to chill a while longer in the fridge though, maybe for an hour or so, before rolling out.