Peel and thinly slice the onion. Rinse the mushrooms and tear them into small pieces, or leave them whole if they are little (like the button mushrooms).

Fill and boil your kettle. Crumble the stock cube into a heatproof jug and add 1/2-1 tbsp horseradish mustard (it's spicy, so use as much or as little as you prefer. You can add more later) and 1 tsp smoked paprika. Pour in 200ml hot water from the kettle and stir to dissolve the stock cube.

Warm a deep frying pan or wok on a high heat. Add the onion and mushrooms to the pan with 4 tbsp cold water. Season with a pinch of salt and pepper and pop on a lid (or use a baking tray if you don't have a lid). Fry on a medium heat, stirring occasionally, for 8-10 mins till the veg have softened and are lightly browned.

While the veg fry, fill a pan with hot water from the kettle. Top up with more water, if necessary and add a generous pinch of salt. Set on a high heat and bring back to the boil. When the water is boiling, add the tagliatelle and simmer for 8 mins till the pasta is tender.

Pour in the stock, pop the lid back on and simmer for 5-6 mins, stirring occasionally, till the stock has reduced a little and the veg are tender. Roughly chop the dill leaves and stalks.

Turn the heat down very low and stir in the soured cream and half of the dill. Warm the stroganoff through for 1-2 mins, then take the pan off the heat, taste and add a pinch more salt or pepper or horseradish mustard if you think it needs it.

Drain the tagliatelle and divide between 2 warm plates or bowls. Spoon over the mushroom stroganoff and garnish with the last of the dill to serve.