In a large saucepan, heat 4 tablespoons of olive oil on medium heat. Add the onion rings to the hot oil and cook for 15 minutes. Do not have the heat set too high because onions burn easily. Spoon the caramelised onions out of the pan and drain them on paper towel. Reserve half to garnish.
Pulse the other half of the caramelised onions in a blender into a thick, dark-brown paste. Add th