Boil water and cook the sweet potatoes with the skin on for 40 to 50 minutes.
Rinse them under cold water and peel them.
Heat oven to 180°C (350°F)
Reduce them to a purée in a bowl and add the butter. Mix well.
Add sugar, milk, eggs, nutmeg, cinnamon and vanilla
Beat with a mixer until the batter is smooth. Then pour the mix over the shortcrust pastry.
Bake for 1 hour
Let cool before serving so that the contents solidify