How to turn pastry scraps into a quick and tasty caramelised onion tart – recipe | Waste not

This simple and on-trend upside-down tart turns leftover trimmings into a fun twist on a French classic

This is my quick version of pissaladière, and it transforms a small amount of leftover pastry scraps into a spontaneous treat. Keep and combine any trimmings into a ball and re-roll as and when required. Pastry keeps well in the freezer, and by skipping two time-consuming steps in the traditional recipe – that is, making the pastry and caramelising the onions – this one comes together about an hour faster. Instead, the onions are cooked upside down, steaming and caramelising beneath a blanket of pastry with anchovies and black olives for a fast, fun twist on a French classic. And if you have less pastry, you can always halve the recipe.