Caramelized onion, ham and gruyere tart

Directions

1. Over a low heat, cook the onions in the butter for a good 60-90 minutes until they've reduced down into a sad looking tangle of onion strings. Lightly season to taste (remember the ham will add salt later)
2. Pop your pastry-crust into a 350 degree oven for 10 minutes (line the base with a piece of parchment paper and weigh it down with dry beans or rice to prevent it rising up). Lower the oven to 325 degrees F once you remove the pastry crust.
3. In a large bowl, mix the 3 whole eggs, 2 egg yolks, heavy cream, mascapone and chives. Season.
4. Spread the caramelized onions over the base of the partially-baked pastry crust.
5. Top the onions with half of the gruyere cheese
6. Add the chopped ham
7. Sprinkle over the remaining gruyere cheese
8. Slowly pour over the egg/cream/mascapone mixture. Be careful not to overfill! You can use a fork to kind of poke around in the filling to make sure the egg mixture gets all the way to the bottom and there are no hidden air pockets.
9. Bake the tart in the oven for 30-40 minutes. If the pastry starts to get too brown, make a little "collar" out of aluminum foil to protect it for the remainder of the cooking time. yourUse a cake tester or skewer to check the interior isn't still super runny. The tart will continue cooking for a little while once you remove it from the oven. Ideally you want a little jiggle when you lightly shake it.
10. Let the tart rest for at least 15 minutes before slicing to serve. Enjoy it warm, at room temperature or straight from the fridge.