For the pastry:
1. Mix the flour and icing sugar together in a bowl. Add the diced butter and rub it in with your fingertips until the mixture looks like fine breadcrumbs.
2. Make a well in the centre of the flour mixture and add the egg. Mix with a spoon and draw the egg into the flour to bring the pastry together. If it’s a little too dry add the water.
3. When the dough begins to stick together, gently knead into a ball. Wrap in cling film and leave to rest in the fridge for 30 minutes.
4. Turn out the dough onto a lightly floured work surface and roll it out into a circle that's about 3mm thick.
5. Line a 20cm loose-based tin with the pastry, leaving the excess pastry hanging over the edge. Prick the base all over with a fork, then chill in the fridge for 15 minutes.
6. Preheat your oven to 200°C.
7. Line the chilled pastry case with baking parchment and baking beans, then bake in the oven for 12-15 minutes, or until the edge ofthe pastry is light golden-brown.
8. Remove the baking beans and paper, and bake for a further 5-8 minutes, or until the pastry case is crisp and golden-brown all over.
9. Once cooled, carefully trim the edge to remove any overhanging pastry and to neaten the edge. Turn the oven down to 150°C.
For the filling:
1. Pour the milk and cream in a pan, add the tea bags and bring to the boil.
2. Whisk the egg yolks with the sugar. Remove the tea bags from the hot cream mixture then pour onto the egg mixture and mix well.
3. Place the trimmed pastry case on a baking tray. Pour the custard into the tart case then sprinkle the nutmeg over the surface.
4. Bake in the oven for 30-35 minutes, or until the custard is just set.
5. Leave to cool at room temperature. Remove from the tin, dust with plenty of icing sugar and slice into wedges.