Fill the kettle and boil it. Pop the porcini into a heatproof bowl. Pour in 150ml hot water from the kettle. Put to one side to soak for 10 mins.
Finely slice the leek. Trim and peel the carrots. Thickly slice them. Trim the leaves and stalks from the kohlrabi, finely chop and keep them to one side. Peel and roughly chop the kohlrabi.
Trim the purple sprouting broccoli. Peel and grate or crush the garlic.
Warm 2 tsp olive oil in a pan. Add the chicken. Fry over a medium heat for 5 mins till the chicken is golden all over. Stir often. Lift out of the pan. Pop to one side.
Add the leek to the pan with 2 tbsp cold water. Season. Cook over a low heat for 5 mins till the leek is soft. Stir often. If it looks like it's going to burn, add more water. Add the garlic. Cook and stir for 1 min.
Pop the chicken back in the pan. Add the carrots, kohlrabi, the porcini and the water they soaked in. Pour in 600ml hot water from the kettle. Cover. Bring to the boil. Turn the heat down. Simmer for 15 mins till the veg are nearly cooked.
Add the broccoli and the kohlrabi stalks and leaves. Simmer for 3-5 mins, without the lid on, till the veg are tender. Taste. Adjust the seasoning. Serve the hot pot straight away.