Bring a large pot of water to the boil. Salt it and blanch the beet greens for 1 minute. Remove the leaves and immediately rinse under ice-cold water to set their color. Gently lay flat on tea towels, and pat dry with another tea towel. They should be completely dry.
Line a buttered terrine mold with a piece of parchment. Neatly lay in the beet leaves to cover the bottom and sides completely. They should dangle over the sides a bit so that they can be folded over the completed terrine later.
Cook the cauliflower, carrots and peas one at a time in the same pot of boiling salted water, until very tender. Remove them and immediately rinse in ice-cold water to preserve their color. Drain well. Roast the pepper until very soft. Peel, seed and cut into pieces.
Heat the oven to 350 degrees F/180 degrees C.
This terrine has five layers, so work one vegetable at a time. First put the cauliflower in the blender with 1/4 cup/60 ml cream and 1 egg. Pulse to a smooth puree. Pour into a small bowl and set aside. Rinse the blender and proceed with the remaining vegetables in the same manner, pouring their purees off into bowls and setting aside. Put the final egg and 1/4 cup/60 ml cream in the blender with the Parmesan cheese and puree to blend. Season each mixture with salt and pepper.
If you pour one mixture on top of the other into the terrine, they will run together, so spoon them in instead. Start with the carrot, spooning it into the terrine and smoothing it out to the edges. Next, spoon over the cauliflower, followed by the peas. Spoon the Parmesan mixture over evenly, and end with the red pepper. If one leaks through to another layer, fear not: some think it is even more beautiful that way and in any case it will taste delicious. Fold the overhanging beet leaves over top to cover. Bake in a water bath until set, a good hour.
Remove the terrine from the bath. Let it cool completely on a wire rack, and, if possible, chill in the refrigerator overnight so it sets well. At least half an hour before serving, turn the terrine out onto a cutting board or platter for serving in slices.