It happens again and again...I buy onions, potatos or garlic in bulk and they start to sprout or perish. Some supermarkets only offer these foodstuffs in larger packages and when given the choice of buying a few individual or a larger package, the larger package seems to be more economic. It certainly is, but then I have to use them before they go off. Some home cooks use yellow onions every day in their cooking, I can sometimes cook for myself without using even one probably for a couple of weeks. There are just too many other kinds of onions: red onions, shallots, spring onions...

The first realisation that helped me tackle the problem of foodwaste in my home was that I have to become aware and identify the usual suspects. In my case it’s bulk buying onions, garlic and potatos. I think I have to make a decision: either stop buying these items in bulk or if I do buy in bulk, make a plan what to do with them before they perish, ideally the moment I come home from the shopping. Currently there is a leftover from a 1.5 kg package of yellow onions I intended to use before they go off. Since it’s early autumn and the season of Federweißer (young wine) has started in Germany, which is traditonally served with onion tart, I decided to create my own decadent version of an onion tart. With the price of butter currently having reached a 15-year high the shortcrust pastry in itself is decadent enough. Rather than using sour cream I was tempted to use stracchino, an Italian soft cheese to introduce a note of bitterness. If you have trouble finding stracchino (good Italian delicatessens should have it), use creme fraiche or sour cream in combination with another cheese, such as grated goats cheese or crumbled blue cheese. Feel free to experiment and explore.

I had about 800 g leftover from my package of onions. If you have less and want to make this tart, I suggest you use the amounts for shortcrust pastry I have given here and make a galette. Galettes are wonderfully rustic. They are perfect if you don't have a large kitchen, you don’t need an arsenal of tart tins of various sizes and they don’t create any leftover pastry that has been overlapping.

On this occasion I would like to thank Astrid Sophie Fleisch for helping me get my shortcrust pastry right every time. I’m giving you a little more detailed instructions here on the pastry making, because I find that lacking in a lot of recipes.

Onion and cheese tart

For the shortcrust pastry

• 180 g flour, sifted

• 90 g cold butter, cubed

• a few tablespoons ice cold water

For the tart filling

• 800 g of yellow onions

• 60 g of butter

• 1 tablespoon olive oil

• 1 egg, lightly beaten

• 1 packet of stracchino

• salt and pepper

Start by making the shortcrust pastry. This is ideally done a day ahead, so it has time to chill in the fridge (otherwise it easily cracks and shrinks). Put the flour in a large bowl and add the cold butter, the smaller the cubes, the better. Fold the butter gently into the flour, use only your fingertips, work swiftly and don’t overwork the dough. You want the texture of fine grains of sand. Add a couple of tablespoons of ice cold water to bring the mixture together. Again don’t overmix. Form the dough into a ball and then flatten to a disc. Wrap in cling film and refrigerate for a couple of hours, ideally overnight.

Peel the onions by first halving them lenghtwise (from the stem down to the root) and then removing the outer layer. Don’t cut off the root end, because that helps you keep the onion together when slicing it. Slice the halves cutside down and discard the root ends. Melt the butter with the oil in a non-stick pan over medium heat. Add the onions, reduce the heat to medium-low and gently caramelize the onions for 20 minutes. They shouldn’t get brown, so keep an eye on the temperature. Remove from the heat, let cool a bit, then gently fold in the stracchino, season with salt and pepper, then add beaten egg.

Heat the oven to 200 ° C (400 ° F). Roll out the pastry on a floured surface to a thickness of around 4 mm (0.15 inches). Since the dough is cold this will take a little while. Don’t press too hard on it, it will get flat. Don’t worry about the rough edges of the rolled out dough. We are making a rustic tart here. Move the rolled out pastry to a baking sheet lined with parchment paper. Distribute the onion and cheese mix over the centre of the pastry dough. Leave a border of around 5 – 7 cm (2-3 inches) at the edge. Fold over the edges and gently press together in the corners, so the pastry holds together. Bake the tart for 30 minutes on a middle shelf. Enjoy with Federweißer or a white wine of your choice.