Taleggio cheese and onion tart

Are you familiar with the Italian Taleggio cheese? Originally made in and named for Val Taleggio near the Swiss-Italian border, this soft cow's milk cheese has been described as

'a  mild stinky cheese, with a whiff of steamed broccoli, almonds and humid cellars' :D

There's a detailed blog post about Taleggio written by David Clark here. It's a beautifully melting cheese that's especially wonderful in various pies and tarts and quiches. I've used it quite often in my cooking, though never blogged about it before (however, there's a recipe for wild mushroom and Taleggio pie in my first cookbook). There are quite a few foodbloggers who have written about it, so you should not have any troubles finding recipes if you're interested (do try Anne's risotto with Taleggio, it's delicious!)

The recipe below is inspired by the British author Nigel Slater, but I've modified the quantities.

Taleggio and onion tart
(Sibulapirukas Taleggio juustuga)
Serves six

6 medium sized onions (or 2 huge salad onions)
50 g butter
500 g (yeasted) puff pastry
200 g Taleggion cheese
handful of fresh thyme

Peel the onions and cut into thin slices. Melt butter in a heavy saucepan, add onions and sauté over low heat for about half an hour, until onions are soft and silky and sticky.
Roll out the puff pastry to fit a small deep baking sheet (mine was 25x34 cm). Using a sharp knife, make an insertion about 2 cm from the edge of the pastry.
Spread the soft and sticky onions over the pastry, leaving the edges clean. Use the onion-flavour pan liquid to brush the pastry edges.
Cut the cheese into slices, dot over the onion filling. Sprinkle some thyme leaves on top.
Bake in a pre-heated 220 C oven for 15-20 minutes, until the pastry is risen and golden, and the onions are nicely golden brown.