You will need a deep baking dish about 28cm long and 18cm wide.
Heat oil in a pan over medium heat. Add onion and 1 tsp salt, cook for 10 minutes. Add garlic and cook for a further 5 minutes. Deglaze with wine, add sugar and cook until liquid almost evaporates.
Add tomatoes, simmer about 20 minutes, until sauce reduces by half. Add pepper.
Peel and chop celeriac into 1cm pieces. Melt 40g butter in a saucepan, then add 1 tsp salt and celeriac. Cook over a low heat, covered, for about 5 minutes. Add cream, then simmer uncovered for about 10 minutes, or until celeriac is tender. Remove from heat and add truffle oil. Place mixture in a food processor and blend until a smooth purée is achieved.
Cut spinach leaves from the bunch, discard stems and wash thoroughly. Heat 40g butter in a frypan, add leek, 1 tsp salt and some pepper. Cook over a low heat for about 8 minutes, until leek is soft. Increase heat, add spinach leaves and cook for 2 minutes until spinach has just wilted. Remove and drain off any excess liquid.
Preheat oven to 190°C.
Place a third of spinach mix into the dish, crumble over 100g goats cheese and spoon over a third of the celeriac mixture. Place lasagne sheets on top then add a third of the spinach, all the tomato sauce and another layer of sheets. Spread over the remaining spinach, 100g of the cheese and one third of the celeriac. Layer the final sheets and finish with the remaining celeriac and goats cheese.
Cook for 30 minutes or until sauce is bubbling. Stand for 10 minutes, then serve.