Nigel Slater’s recipes for roast onions with polenta, and cheese and onion tart | Food

I have been cooking a pan of onions for a good half an hour, stirring them from time to time, while I potter about making pastry. They have gone from crisp to soft, ivory to walnut and, more importantly, from pungent to mild and sweet.

There is no point in hurrying an onion – other than those you dip into batter and dunk into bubbling oil. They need time and that is what they are getting today. Later, when they are glossy and translucent, they will join eggs and cream, and mustard and cheese in a pastry case – the second of two cheese and onion suppers this week. This one will sit with a spinach salad and perhaps some speckled Castelfranco and a few segments of citrus.

Winter is the best time for cooking onions. Stored for several months, their flesh contains less water, and so produces less steam as they cook. Without excess moisture, they brown more effectively. Some sticky Marmite-like goo will appear on the pan and that is all to the good. Stir it in so it can gently stick itself to the glossy alliums. For this tart, they are ready when you can squish them effortlessly between your thumb and finger.

There were more onions in the oven yesterday, this time toasted on one side, left to bake for the best part of an hour, then brought to the table on a bed of soft and cheesy polenta. When it comes to cooking onions, it is best to take the scenic route.

Roast onions, gruyère polenta

The onions need to be soft right through to their heart. Pierce them with a metal skewer to check. If the cut edges have browned here and there, so much the better. Serves 4

onions 4, small to medium
groundnut or vegetable oil 4 tbsp

For the polenta:
water 500ml
milk 250ml
coarse polenta 125g
gruyère 75g, grated (or a good sharp cheddar)
butter 50g

For the crumbs:
groundnut or olive oil 2 tbsp
fresh white breadcrumbs 60g
parsley leaves a good handful, chopped
dill fronds 2 tbsp, chopped

Preheat the oven to 200C/gas mark 6. Peel the onions, cut them in half and place them cut-side down in a large roasting tin. Trickle over the oil, season with salt. Bake for 40 minutes until the undersides are nicely toasted, then turn the onions and cover with foil. Return to the oven for a further 20 minutes. They must be tender and nicely golden-brown. If there are some caramelised juices in the tin that is good news – we will use them later.

When the onions are almost done, make the polenta. Bring the water and milk to the boil, add 1 tsp of salt and lower the heat so the liquid simmers. Pour in the polenta either from a jug or rain it in a steady stream with your hand (if you add it in one go it will form lumps). Stir immediately, taking care to guard your hands from the Vesuvius-like bubbling that ensues. Lower the heat, so the simmering is really slow and gentle, then stir regularly for 25-30 minutes.

Make the crumbs: warm the oil in a shallow pan, then tip in the breadcrumbs. They will fizz in the oil. Toss them around a little so they colour evenly. They need to be lightly crisp and a deep golden colour. Stir in the chopped parsley and dill.

Stir the cheese and butter into the polenta and season. I like to include a grinding of black pepper at this point. Ladle the polenta into a serving dish, place the roasted onions on top, then trickle over any roasting juices from the tin. Scatter with the toasted breadcrumbs.

Cheese and onion tart

There is something of the Welsh rarebit about this tart, so feel free to use even more mustard if you wish. It is good with a winter salad, such as spinach and orange. Serves 6

For the pastry:
plain flour 150g
butter 80g
egg yolk 1
iced water 1-3 tbsp

For the filling:
onions 3, large, about 750g
butter 50g
olive oil 2 tbsp
egg 1, large
egg yolks 2, large
whole grain mustard 1 tbsp
double cream 250ml
cheddar 125g, grated

You will need a 20cm tart tin with a removable base. Make the pastry by processing the flour and butter to fine crumbs. (Alternatively, rub together the butter into the flour with your fingertips until it resembles breadcrumbs.) Mix in the egg yolk and a tbsp or two of iced water to form a thick, rollable dough.

Tip the dough on to a lightly floured board, pat into a thick disc then wrap in baking parchment and then rest it in the fridge for 30 minutes.

Make the filling: peel the onions and cut into thin segments. Warm the butter and oil in a deep-sided pan over a moderate heat, add the onions and let them cook, stirring regularly, for a good 30 minutes. This seems like a long time, but the slow cooking will leave the onions particularly soft and sweet. Stir them every few minutes, making sure to stir in any sticky caramelised sugars that form at the bottom of the pan.

Remove the pastry from the fridge and place on a floured board. Roll it out to fit the tart case. Lower the pastry into the tart tin, pushing it gently into the corners and up the sides. Trim any overhanging pastry, then rest the pastry a second time, in the fridge or freezer, for 20 minutes. I know this sounds like a drag, but it will prevent the sides shrinking as it cooks.

Set the oven at 190C/gas mark 5 and place a baking sheet in the oven. You will bake the tart on top of this.

Fill the pastry case with parchment and baking beans, then place on the baking sheet already in the oven. Bake for about 20 minutes, then carefully lift out the paper and beans. If the pastry isn’t dry to the touch, return it to the oven for a few minutes, then remove and set aside.

Turn the oven down to 180C/gas mark 4. Mix together the whole egg and yolks with a fork, then stir in the mustard, cream and cheese, a little salt and pepper, then stir into the onions. Grind in a little black pepper, then fill the tart case with the mixture. Bake for about 30 to 35 minutes until the surface is golden. Leave to settle for at least 20 minutes before slicing.

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