Pre-heat the oven to 200°C. Roll out the pastry on a lightly floured surface to 1cm thick and cut rounds of pastry slightly larger than the individual fluted flan tins. Line the flan cases using the pastry, pressing in well and prick the bases. Trim any overhanging pastry and chill for 10 minutes. Line the pastry cases with nonstick baking paper and fill with baking beans. Bake in the oven on a baking sheet for 10-12 minutes until golden. Remove the paper and beans at this point, brush the bases with the beaten egg yolk and return to the oven to allow the base to cook and brown. Meanwhile, make the filling by whisking the crème fraiche and the cream together. Beat in the eggs one at a time and season well with salt and pepper. Heat the sunflower oil in a large pan over a medium-high heat and wilt the spinach in batches. Drain the spinach in a colander placed over a bowl and squeeze out as much of the liquid from the cooked spinach. Combine with the filling mixture. Remove the pastry cases from the oven and pour the filling into each one so that it comes almost all the way up. Place a disc of goat's cheese in the centre of each and bake in the oven on a baking sheet for 20 minutes or until the filling is set and the goat's cheese is golden brown.