Meanwhile, peel the swede and cut into 1cm dice. Melt the butter in a saucepan and add the swede, thyme and some salt and pepper. Cover and cook over low heat, stirring regularly so it cooks evenly, about 20-30 minutes or so, until soft
The swedes are cooked when they are golden and tender.
Whilst the swede is cooking, cut the sourdough into very small cubes, and spread out over a baking tray and toast in the oven for 8-10 minutes until crisp. Take out and leave to cool. Keep the oven on.
Cut the peppers in half lengthways, leaving the stalks on. Remove the seeds and white membrane, and place cut-side up on a baking sheet lined with baking parchment or aluminim foil.
Once the swede is cooked, remove from the pan from heat. Add the toasted bread, garlic, capers and cheese, season with a little salt and pepper, and mix well.
Stuff inside the peppers, pushing the filling in well and piling it up slightly high (the filling will shrink upon cooking). Place prepared peppers on a baking tray lined with parchment paper or a baking sheet.
Place the tray with the peppers in the middle shelf of the oven and bake for 10 minutes, until the peppers are beginning to be charred at the edges. Then turn down the oven to 200C (180C fan) and cover the peppers loosely with aluminium foil and bake for 20 minutes more. The peppers need to be soft.
To serve: Before serving, sprinkle with grated gruyere and chopped parsley, and return to the oven for a couple of minutes to melt the cheese.