Start by melting the butter in a medium skillet, add the onions and sprinkle them with the brown sugar. Add the balsamic vinegar , salt and pepper. Simmer the onions until they become light brown and quite sticky.
Place each short pastry disc in a tartlet ramekin or tart pan, add a tablespoon of caramelised onion and then sprinkle with some fresh thyme leaves.
Bake the tartlets for 30-40 minutes in a preheated oven at 170º C.
When the pastry is ready and the onions bubbly, place some halloumi cheese on top of the tartlets and put them into the oven for 5-10 minutes. Add some more fresh thyme, fresh mint leaves and enjoy with a glass of cold beer!