First, add the 400 ml red wine, and bay leaves into a saucepan, bring to the boil, and boil for 5 minutes. Season with freshly milled sea salt and black pepper, stir well and leave to cool.
Combine the chunks of beef, grated garlic and bay leaves in a large bowl and cover with red wine. Season with black pepper and sea salt, mix thoroughly, cover with cling film and, if possible, refrigerate the marinade overnight.
Set aside a large casserole dish (with lid), then fire up a large frying pan on a medium heat, add 1x tbsp of olive oil, then cook the red and white onions together until soft and lightly browned. Place into the casserole dish.
Drain the red wine from the marinade in a colander, and save it for later. Next, gently heat up another tbsp olive oil, and add a tbsp of paprika. Be careful not to burn it. The aim is to give the oil a great colour and flavour. Then, in batches, seal off the chunks of beef and place in the casserole. Repeat the previous step with the paprika and oil, until all the meat is cooked.
Preheat the oven to 180C.
Next, add the reserved red wine marinade to the frying pan, the goulash paste, tomato puree and water, and slowly bring to the boil.
Crumble in the stock cubes and gently whisk into the sauce.
Meanwhile, add the chopped tomatoes, peppers, parsley, and tomatoes to the casserole dish and mix thoroughly. Also (optional) add the chillies to the dish
Once the stock has reduced and thickened slightly, pour over the the other ingredients, mix thoroughly, and cover with a lid.
Cook, in a middle oven for 30 minutes, then reduce to 140C and continue for a further 2.5 hours.
After an hour of cooking, add the celery and carrots and sir through, then return to the oven.
Keep an eye on the goulash, and stir occasionally.
Add the mushrooms, and continue to cook for a further 45 minutes.