Preheat oven to 100C.
In a food processor place flour, butter and salt and process until the mixture resembles breadcrumbs.
Add water and continue to process until dough forms a ball.
Turn off processor and remove dough.
Cut dough into 4 pieces, cling wrap and refrigerate for ½ an hour - 1 hour.
Remove dough from refrigerator and place on lightly floured work surface. Using a rolling pin roll each ball to 0.5 cm thick.
Grease individual tart tins with a little butter and line tins with pastry.
Place greaseproof paper over pastry and weigh the paper down with beans or rice.
Place tart tins on a sheet tray and bake in the oven for 15 minutes.
Remove the weights (i.e. beans or rice) and paper and cook for further 10-15 minutes.
Place a medium sized sauté pan over a medium to high heat and drizzle a little olive oil and add shallots and mushrooms and sauté for 1-2 minutes.
Add spinach and continue to sauté for further 1-2 minutes.
Once spinach has wilted and mushrooms are soft remove from heat and allow to cool.
Divide spinach, mushrooms, and cheese between the tarts.
In a separate bowl combine eggs and cream and whisk gently with a fork.
Pour over egg and cream mixture (be careful not to overfill) and return tray to oven.
Bake for 15-20 minutes or until just set.
When removing tarts from oven allow to cool for 5 minutes before unmolding.
Cut into quarters and arrange on a serving dish.