Add the butter, flour, sugar and egg to the electric mixed, and whisk at medium speed until you have a soft dough. Cover with cling film and leave to stand for about one hour.
Roll out the dough and place it in a tart tin. Cut off the excess and cover the tart with parchment paper. Fill the tin with dried beans and bake in the oven for 15 minutes. Remove the beans and paper, and bake for another 10 minutes, until golden brown. Remove the tart from the oven and leave to cool.
In a water bath, boil the can of sweetened condensed milk for two hours. Open the can and check that the condensed milk has taken on a caramel colour.
Bring the cream to a boil. chop the chocolate, place it in a large bowl, pour the hot cream and condensed milk over it and mix until you have a smooth mixture.
Sprinkle half the pecans on the tart base, and cover with the chocolate mixture. Place in the fridge for 30 minutes (covered with cling film) or on the counter top overnight. Decorate with the rest of the pecans and some chocolate glaze.