Heat the butter with the oil in a pan over a medium heat. Fry the onion and garlic for 3-4 minutes, or until softened, stirring occasionally.
Add the sliced mushrooms to the pan and cook for 2-3 minutes.
Add the wine to the pan and bring to the boil. Reduce the heat until the mixture is simmering. Continue to simmer until cook over a high heat until the volume of liquid has reduced by half.
Stir the cream into the pan and season with salt and freshly ground black pepper, to taste. Return the mixure to a simmer.
Stir the chives and spinach leaves into the mixture until they are warmed through and wilted.
To serve, place one cooked lasagne sheet on a plate and spoon the mushroom mixture on top. Place the remaining sheet on top of the mushrooms and sprinkle over the cheese. Place the lasagne under a hot grill until the cheese is bubbling and golden-brown. (Alternatively, use a cook's blowtorch to melt the cheese.)