(vegetarian, and can be made gluten-free)
This makes a really substantial supper dish, perfect for winter teatimes.
Sauté some thinly sliced onions with a little raw caster sugar to enhance the sweetness. Let them turn soft and lightly caramelised. Put these aside, and blitz black olives and rosemary in a food processor into a chunky paste.
Prepare an ovenproof dish by brushing with a little olive oil. Peel large, floury potatoes and slice as thin as possible - a food processor is probably best. Take a sheet of lasagne, spread some of the olive paste over it and lay in the dish. Once the olive-smeared lasagne sheets cover the base of the dish, spoon over some of the onions. Onto these, place a layer of overlapping potato slices. Repeat the layers until the dish is full and the ingredients are used up - the uppermost layer should be potatoes.
Whisk together double cream, milk, crushed garlic, finely chopped sage, grated Parmesan and Gruyère, and pour the mixture over the lasagne layers.
Cover the dish with foil and bake in the oven. For the last 20 minutes, remove the foil and scatter over some more grated Parmesan to form a bubbly golden cheese crust. Serve with fresh bread (we made honey brioche rolls) and a crisp salad.