Heat a large saute pan over a high heat and add the sausage meat. Use a spatula to break it up into small chunks, then fry for 7-8 mins until golden brown. Remove from the pan with a slotted spoon, leaving the fat behind, and set aside in a bowl.

Turn the heat down to medium. Chuck the butter into the pan and add the leeks and fennel, frying for 5-6 mins until softened but not coloured. Add the garlic and the herb sprigs and cook for 1 min until fragrant, then season with salt and pepper.

Spoon the flour into the vegetable mixture and stir to combine. Cook out for 3-4 mins, stirring regularly, until thickened. Gradually add the chicken stock, bringing to the boil between each addition and ensuring everything is mixed in. Keep going until you've added all the stock.

Stir in the double cream, chuck in the spinach to wilt, then give everything a good mix to combine. Season generously and add a grating of nutmeg to taste. Add the sausage meat back to the pan and fish out the whole herbs to discard.

In a separate bowl, stir together the ricotta, lemon zest and a large pinch each of salt and pepper.

To assemble, divide the sausage filling and ricotta between your ovensafe dishes, layering them up between lasagne sheets (start with a layer of sausage filling, then pasta sheets, then ricotta and so on, then finish with a layer of ricotta). Sprinkle with equal amounts of cheese.

To enjoy now, preheat the oven to 200c/180c fan. Place the lasagne on a baking tray (to catch the drips) and pop it into the oven to bake for 45-50 mins until the pasta is cooked through, the filling is bubbling and the top is golden (cover with foil if at any point the top seems to be browning too quickly). Leave to stand for 10 mins before serving.