Chop the butter into small cubes, then process with the sugar in a food processor or planetary for a few minutes until the mixture resembles breadcrumbs. If you don’t have a food processor gently work the butter into the sugar with your finger.
Work in the egg, then add the vanilla extract, then salt and pulse for a few minutes.
Add one spoon at a time the sifted flour and work until the dough starts to clump together, but don’t work it too much.
Turn the dough to a lightly floured surface and form into a ball, then cover with plastic wrap and chill in the fridge for at least 3 hours.
Take the dough out of the fridge and roll it out on a lightly floured surface into a circle, reserving some dough aside for the lattice.
Roll the dough up around the rolling pin and unroll it into a greased and floured 23 cm tart pan. Trim the edges of the pastry with a knife or rolling over the rolling pin.
Preheat the oven to 180 C°. Prick the pastry case with a fork.
Lightly melt the Nutella in a heatproof bowl set over a saucepan of gently simmering water or put it into the microwave at a low temperature for a few seconds.
Add the double cream, gently mix and spread into the pastry.
Roll the other dough into a circle. Cut 1 cm strips wide using a sharp knife or pizza cutter.
Carefully thread the strips over and under one another, pulling back strips as necessary to weave.
Press the edges of the strips into the bottom pie crust edges to seal. Use a small knife to trim off excess dough
Bake the tart for 30/35 minutes.
Leave to cool in the tin.