Preheat oven to 400°F.

Combine all Roasted Mushroom Conserva ingredients in 9x13 baking pan.

Roast in oven for 25-30 minutes.

Cut onions paper-thin and salt them (just like seasoning) for a few hours.

Squeeze out the moisture from the onions with paper towel and throw them in a pan with a thin coating of oil.

Add a pinch of baking soda and let them go for an hour, scraping them down and deglazing as they stick. When in a rush, add some brown sugar to wards the end to help finish off the caramelization process quicker.

Once onions are caramelized, mixed in herbs of choice, if you would like.

Blend the mushroom and caramelized onions together in a small bowl.

Spread the mixture onto two slices of bread and place cheese between the slices.

Smear mayo on the outside of the bread slices.

Use a panini grill, grilled cheese press or fry the sandwich in a saute pan over medium heat until browned and cheese is melted.