Pre heat oven to 180°C Cook the cauliflower and broccoli in boiling salted water for about 10 minutes.
Soak the lasagna sheets in hot ( not boiling ) water to soften. If using fresh lasagna sheets skip this step.
Mix the creme fraiche with 3 tbsp of water anf the herbs. Season with salt and pepper.
Brush an ovenproof dish with oil and pour in 3 tbsp of creme fraiche. line a third of the lasagna sheets, followed by half of the broccoli/cauliflower, half the ham, half the tomatoes, a third of the cheese and a third of teh creme fraiche sauce.
Repeat the layers, finishing with a layer of pasta. Pour over remaining creme fraiche and sprinkle with the remaining cheese.
Bake for 40 minutes, then grill the top under a grill until it browns and bubbles. If you don't have a grill just bake an extra 10 minutes at 190°C.