Add the oil and sliced onion to a small pan and fry very slowly on a low heat for 30-40 minutes until caramelised.
Add the salt and pepper, balsamic glaze and Worcester sauce. Set aside.
Add all the ingredients to a food processor or high-speed blender, then blitz until very smooth and creamy.
Slice the toast into small slices.
Top with the cheese mix, then pop under the grill until the top starts browning. Serve topped with the caramelised onions.