Heat a large pan, add the butter and melt. Add the onion and fresh thyme and gently cook (30-45 mins) over moderate to low heat until soft. They should be translucent, golden and sticky.
Roll out pastry as thin as possible (to €1 coin thickness) between 2 sheets of cling film. Using your rolling pin, gently lift pastry (still wrapped in cling) and hold over tart tin. Peel off bottom cling layer and gently lower pastry into tin, then press lightly in and around edges of tin. Trim and neaten the edges, holding back a little extra pastry for shrinkage. Line pastry with parchment paper and fill with dried rice or beans. Place in oven at 150 C for 15 minutes until pale and golden. Remove from oven, discard paper and beans, place back in the oven for another 5 minutes, remove again and allow to cool before adding the filling.
Crack eggs in a medium-sized mixing bowl, add the cream and lightly mix with a hand blender. Cut the Camembert into small pieces, then add to the eggs along with the Ricotta, grated Parmesan and seasoning. Lightly blend mixture again with the hand blender until it resembles egg custard. Set aside.
Spread the caramelized onions over the cooled tart base right up to the rim. Arrange 2/3rd of the figs in a neat circle on top of the onions until the tart surface is covered, then pour the egg custard into the tart case. Top with the remaining figs in whatever pattern your heart desires!
Gently transfer to oven - middle shelf - and bake for 35-45 minutes or until cooked and lightly golden. Cool before slicing.