Take the pastry out of the fridge and leave it at room temperature for 10 minutes before rolling it out.
Whisk the egg and then add the cream (or milk), salt, pepper, nutmeg and the grated cheese. Mix well and keep it aside.
On a lightly floured surface, roll out the pastry slightly larger than the pie dish, large enough to cover the bottom and sides of the tin.
Carefully place the dough into an 8" (20cm) fluted tart pan. Tuck it in with your fingers, making sure it is completely smooth.
Prick the dough all over with a fork, cover and place it in the freezer for at least 15 minutes (or fridge for 30 minutes). This helps to reduce pastry shrinkage when cooking.
Preheat the oven to 360 °F (180 °C).
Line the tart tin with parchment paper or tin foil, covering the edges to avoid them from burning.
When the oven is hot, fill the pastry with dried chickpeas or pie weights to prevent the dough from rising and bake for about 15 minutes.
Remove the chickpeas or pie weights and cook for another 8-10 minutes until golden brown.
Remove crust from the oven and let it cool down for 10 minutes before filling it up with spinach and salmon. You can do this stage up to 3 days ahead of time. Cover cooled crust tightly and refrigerate until ready to fill.
Reduce the oven temperature to 350 °F (175 °C).