Soak the ham in water for 2 hours to remove excess salt.
Cut a slit halfway through the onion and place the thyme and bay leaves in the slit.
Press the cloves and allspice berries into the onion.
Insert a thermometer into the ham, making sure it hits the core, and place the ham in a large pot covered with cold water together with the onion.
Bring to a boil and skim off the foam.
The ham is done when the internal temperature reaches 75°C.
Lift out the ham and pull off the rind if you do not want the fat.
Preheat the oven to 225°C.
Place the ham in an oven-safe dish with the fat side up.
Mix the mustard and egg yolk.
Spread the mixture over the ham.
Bake in the middle of the oven for 10 to 15 minutes until it has a nice golden color, watching so it does not burn.
