Peel, trim, halve and finely slice the onions using a mandoline, sharp knife or the slicing attachment on a food processor. Peel the garlic and roughly crush it with the flat of a large knife.

Put a large, heavy-bottomed pan or pot for which you have a tight-fitting lid on a low heat, add the oil and butter, immediately followed by the onions, herbs (if using), garlic and a pinch of salt.

Stir to coat the onions with the oil, then clap on the lid and leave to cook, stirring occasionally, for about an hour, or until they’re very soft.

Meanwhile, if you’re making a bread dough base, stir the flour, salt and yeast in a large bowl, then add the oil and just enough water (probably a little under 150ml) to bring it together into a coherent, but not sticky or floury dough.

Tip out on to a lightly oiled surface, oil your hands, and knead the dough until it’s springy, smooth and elastic. Lightly oil the bowl, put the dough back in, cover and leave in a draught-free place until it’s roughly doubled in size – this should take about 90 minutes, but judge by eye rather than time.

Take the lid off the onions, turn up the heat very slightly and cook, stirring frequently to ensure they don’t catch, until the liquid has evaporated and the onions have turned a light golden brown. Take off the heat and leave to cool.

Lightly oil a baking tray and heat the oven to 200C (180C fan)/390F/gas 6.

Knock the air out of the dough, then, on a greased surface, roll it out into a roughly ½cm-thick rectangle. Spread the onions in a thick layer on top, leaving a border all around the edge.

Cut the anchovies in half lengthways, to make thin strips, use these to create a diamond pattern all over the top of the onions, then pop an olive in the centre of each diamond.

Bake the pissaladière for about 20-25 minutes, until the crust is golden. Drizzle with a little extra-virgin olive oil and leave to cool slightly, or entirely, before slicing and serving.