To make the sofrito: Place all ingredients in a food processor and process to a pesto consistency. Heat a 30cm fry pan or paella pan on high heat.
Add sofrito and cook until tomatoes start to become juicy, 3-4 minutes. Add Flat Mushrooms, Mushroom stock and bring to the boil.
Sprinkle in rice and reduce to a medium heat. Continue cooking for about 16-18 minutes. Do not stir! When rice is tender and liquid has almost fully reduced (there should still be some liquid in the paella-pan), cook for a further 2 minutes to achieve ‘soccarrada’ (crust on the bottom of the pan).
Season to taste with salt and freshly ground black pepper and garnish with chives, thinly sliced button mushrooms, radish and grated manchego cheese.
Squeeze over lemon juice just before serving.