Celeriac & Spinach 'Stamppot' with Farmer's Sausage

Melt a third of the butter in a frying pan over medium-high heat. Fry the sausage for 3 - 4 minutes until evenly browned, then cover with the lid. Fry for 8 - 10 minutes over low heat, turning regularly.

Slice the onion into half rings. Halve the mushrooms or cut any larger ones into quarters. Take the sausage out of the pan and set aside. Add another third of the butter to the same pan and fry the mushrooms for 5 - 7 minutes over high heat. Lower the heat, add half of the onion and fry for 3 more minutes. 

To the mushrooms, add the mustard and the water, then crumble in the stock cube (see pantry for amounts). Allow to reduce for 5 minutes so as to make a jus, then add the sausage and allow to simmer for 3 minutes. Meanwhile, heat a drizzle of olive oil in a frying pan over medium-high heat. Fry the rest of the onion for 2 - 3 minutes, then gradually add the spinach and allow to wilt and reduce.

In the meantime, mash the potatoes and celeriac with a splash of milk and the rest of the butter. Add the Belgian spice mix and the spinach, then mix well to combine and season to taste with salt and pepper.