Preheat the oven to 200°C (392°F) top/bottom heat (fan 180°C (356°F). Melt the vegetable fat in a casserole dish over a high heat. Sear the meat all over, remove and set aside to cool down a little. Mix the mustard and pepper together in a small bowl and used to brush the meat. Lay the bacon rashers on top of the meat so that it is com-pletely covered.
In a larger bowl, mix together the flour, 1½ tbsp of Herbes de Provence, sea salt and ordinary salt. Separate the eggs, add the egg whites and about 150 ml of water to the dry ingredients. Knead all ingredients into a tight dough, adding a little more water or flour if needed.
Roll the dough out onto a work surface dusted with flour, place the meat on top and cover completely. Arrange on a baking tray. Beat the egg yolk and use it to brush the surface of the dough, sprinkle over the rest of the Herbes de Provence. Cook the meat in the preheated oven on the middle shelf for 45 minutes. Allow to cool on a wire rack before carving.