2) While potatoes are cooking, add the bacon to a large saute pan and cook over a low/medium flame. When the bacon is cooked remove with a slotted spoon and drain the fat, reserving some if you want to add it later.
3) Wipe the pan with paper towels and turn up the heat. Add a good amount of rapeseed oil and heat until you see some smoke. Once the oil is hot, carefully add the potatoes and shake the pan a couple of times to prevent sticking.
4) Turn down the heat a little and let the potatoes brown. Season with salt and pepper. After a few minutes, shake the pan and turn potatoes to brown on all sides.
5) When the potatoes are almost completely cooked, add the red onion and let everything cook together. Once the onions are caramelised, add the capers and deglaze with red wine vinegar.
6) When the vinegar is mostly evaporated, add the extra-virgin olive oil, mustard and bacon (and reserved bacon fat if you wish). Re-season with lots of freshly-ground black pepper. Serve warm.