Pre-heat the oven at 180 °C.
In a thick bottom pan add butter, onion, olive oil & sugar. Allow it to cook covered on slow flame for 20 mins for caramelization. Stir in between, though take care and not break them up too much. Add oregano set aside.
Steam broccoli & corn in microwave using a microwave steamer or electric steamer or pass them through salted boiling water for a couple of mins.In a large pan, add white sauce and 100 ml cream. Bring to a boil, add 1/2 cup cheese, salt & pepper. Allow it to cool.
Gently fold in broccoli, corn & remaining cream.Fill the mixture in the cooled pastry crust. Spread remaining 1/4 cup cheese on top. Fill a small baking try with hot water & place it in the bottom of the oven. I used a small tart mold & placed it next to the quiche only as I bake in microwave/ convection oven. (this will keep the environment moist so the quiche won't dry out)
Place your quiche on the middle rack and bake for 35 mins until almost golden. Turn the oven off and open the door for few minutes to let the steam escape.
Now close the door & leave the quiche inside for 2 hours. Once the quiche is cool, remove from oven and wrap in cling film. Refrigerate for 7-8 hours. You can eat warm as well, if that's what you like but this quiche really tastes out of world when cold.
Remove. Trim the excess pastry and devour.