Luxurious Nutella Tart

Whisk the egg and vanilla together in a small bowl; set aside.

Process the hazelnuts and sugar together in a food processor until finely ground, 8 to 10 seconds.

Add the flour and salt and pulse to combine.

Scatter the butter pieces over the top and pulse until the mixture resembles coarse cornmeal, about 15 pulses.

With the machine running, add the egg mixture through the feed tube and continue to process until the dough just comes together around the processor blade, about 12 seconds.

Turn the dough onto a sheet of plastic wrap and flatten into a 6-inch disk. Wrap the dough tightly in plastic wrap and refrigerate for 1 hour or up to 2 days.* Before rolling the dough out, let it sit on the counter to soften slightly, about 10 minutes.

Roll the dough out to an 11-inch circle on a lightly floured counter, loosely roll around the rolling pin, lift, then carefully fit it into a 9-inch tart pan with removable bottom. Trim access dough using a sharp knife to make a clean edge. Use access dough scraps to press into any weak, thin areas.

Set the tart on a large plate and freeze the tart shell for 30 minutes.

Adjust oven rack to middle position and heat oven to 375F/190C.

Set the tart pan on a large baking sheet. Press a double layer of foil into the frozen tart shell and over the edges of the pan and fill with pie weights or dried beans, uncooked rice or pennies.

Bake until the shell is golden brown and set, about 30 minutes, rotating the baking sheet halfway through baking.

Carefully remove the weights and foil and continue to bake until it is fully baked and golden, 5 to 10 minutes longer.

Transfer the baking sheet to a wire rack and let the tart shell cool on the baking sheet while make the filling.

Cook the hazelnuts and sugar together in a medium nonstick skillet over medium heat, stirring constantly until the nuts are golden and caramelized, about 1 minute. Remove the nuts from the skillet and set aside in a small bowl to cool.

Bring the cream to a brief simmer in a saucepan over medium-high heat. Off the heat, stir in the chocolate and butter, cover the pan, and let stand until the chocolate is mostly melted, about 2 minutes. Gently stir the mixture until smooth. If the mixture looks grainy with bits of chocolate, reheat it gently over low heat, whisking constantly until completely smooth.

Stir in the Nutella. It will be clumpy and difficult to stir at first, but then it will smooth out as the stirring progresses.

Sprinkle the cooled candied hazelnuts over the bottom of the tart shell, breaking up any clumps.

Pour the chocolate filling evenly over the nuts, cover tightly with plastic wrap, then refrigerate the tart until the filling is firm, about 2 hours or up to 1 day.

Uncover the tart, then pour on the glaze (if using, instructions below) and tilt the pan to cover the top completely. Smooth out with a spatula if needed.

To serve, remove the outer metal ring of the tart pan, slide a thin spatula between the tart and the tart pan bottom, and carefully slide the tart onto a serving platter. Serve cold or at room temperature.

Whisk together the Nutella and milk until silky smooth. If the Nutella hasn't completely dissolved at the point, then heat in the microwave for 10 seconds and whisk again.