Preheat the oven to 190C / gas 5.
Boil the Romanesco cauliflower and broccoli for 5 minutes, then drain, reserving the cooking water.
Heat 3 tbsp oil in a large pan and add the garlic, thyme, anchovies and chilli flakes if using.
Allow the anchovies to melt, then stir in the drained florets and 4-5 tbsp of cooking water.
Cover partially with a lid and cook very gently for around 20 minutes until the vegetables are very tender and intense in flavour.
Lightly crush and season, then leave to cool.
Lay 4 of the lasagne sheets in a generously buttered baking dish.
Stir the ricotta and half the parmesan into the cooled vegetables then spread half the mixture over the pasta.
Top with 4 sheets of pasta, repeat and finish with a layer of pasta.
Place the sliced mozzarella and parmesan over the top of the pasta, drizzle with oil and bake for about 30 minutes, until bubbling and golden.
Serve hot or warm.