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RINSE the leek, remove the outer leaves and a part if the greens leaves. Coarsely CHOP the leek, peel the carrots and also coarsely chop them.
PEEL and finely chop the onion and garlic cloves. RINSE the potatoes, there's no need to peel them. CHOP the meat into bite-size pieces and coat them with flour, pepper and salt.
Heat a knob of butter in a skillet and cook the stewing meat in batches until they're beautiful brown. ADD the meat to the slow cooker along with onion, garlic, carrots, fennel, potatoes, leek and bay leaves.
DEGREASE the skillet using red wine, this way all the meat flavours will end up in the slow cooker. STIR the mustard into the red wine along with beef stock. POUR the mixture into the slow cooker and set to the lowest setting for about 5 hours.
You can also create this stew in a Dutch oven, it's best to sauté everything before you'll add the liquids and let it simmer for about 1,5 hours.
SEASON the stew with pepper and salt and remove the bay leaves before serving. Enjoy!