For the pastry
Mix all the pastry ingredients in a mixing bowl and knead to a smooth dough. Shape into a ball, put on a plate, brush with oil, cover and leave to rest for about 30 minutes.
For the filling
Heat the butter and gently cook the leek and onion until translucent.
Blanch the cabbage, mangetout and carrots in salted boiling water for 3 minutes, then rinse in cold water and drain well.
Mix the crème fraîche with the egg yolks and parsley. Stir in the vegetables and season to taste with salt, pepper and nutmeg.
Heat the oven to 200°C (180° fan) 400°F gas 6. Grease a baking tray.
Roll the pastry out to a rectangle on a floured tea towel, then stretch over the backs of your hands until wafer thin. Spread the pastry out on the tea towel and cut off any thick edges.
Sprinkle with breadcrumbs and lay the slices of ham on the pastry. Spread the filling on top of the ham.
Fold in the left and right edges of the pastry, then loosely roll up the strudel using the tea towel to help you. Place join side down on the baking tray and brush with melted butter.
Bake for 30-40 minutes until golden and crisp.
Place on a serving plate and cut into slices to serve.