Peel, trim, halve, and dice <quantity>2</quantity> large onions

Add <quantity>⅓<unit>cup</unit></quantity> of extra virgin olive oil to a skillet over medium heat

Add the diced onions to the skillet. Lower the heat and cook for 15m, stirring occasionally until caramelized

Add <quantity>½<unit>cup</unit></quantity> of brown sugar. Melt the sugar on top of the onions without stirring

Add <quantity>½<unit>cup</unit></quantity> of balsamic vinegar

Simmer over low heat for 7-8m, stirring occasionally until the mixture thickens

Transfer the mixture to a blender and blend on high speed until creamy, but still with the onion texture. Transfer to another recipient and let it cool down. The balsamic onion jam is ready

Chop <quantity>⅓<unit>bunch</unit></quantity> of chives

Melt <quantity>½<unit>tbsp</unit></quantity> of the butter in a saucepan over medium heat until lightly browned

Halve <quantity>1</quantity> potato bun and toasted in the saucepan rubbing it to absorb the butter. Remove from heat

Trim <quantity>200<unit>g</unit></quantity> of oyster mushrooms

Melt <quantity>½<unit>tbsp</unit></quantity> of butter in a saucepan over medium heat

Add the mushrooms and season with salt and pepper to taste

Cook the mushrooms for 7m, stirring occasionally until they are brown

Add <quantity>½<unit>tbsp</unit></quantity> of butter to the side of the saucepan. Add <quantity>¼<unit>cup</unit></quantity> of spinach and cook until it reduces in size and gets a deep green color. Remove from the heat and set aside

Preheat the oven to <temperature>180<unit>°C</unit></temperature>

Crack <quantity>3</quantity> eggs and place in a bowl. Whisk until they are liquid and even in color

Add <quantity>1<unit>tbsp</unit></quantity> of heavy cream and whisk until fully combined

Melt <quantity>½<unit>tbsp</unit></quantity> of the butter in a saucepan over medium-low heat and spread over the entire surface

Pour the eggs into the pan and season with salt to taste

Season with black pepper to taste and add the chopped chives

Cook until the sides of the omelet begin to set and the center is still slightly runny. Fold the omelet with a spatula. It's okay if it gets a little messy

Place <quantity>2<unit>slices</unit></quantity> of cheddar cheese on the toasted bun. Add the omelet on the bottom side

Add the mushrooms and the spinach

Add spicy mayonnaise and the Balsamic Onion Jam to taste

Wrap the sandwich in parchment paper

Cut in half and add <quantity>1<unit>slice</unit></quantity> of cheddar cheese, cut in half, on each side

Place the sandwich in a skillet or a baking tray, with the cheddar cheese facing up. Place in the oven and broil until the cheese is completely melted. The veggie egg & cheese sandwich

Dig into this veggie and flavorful sandwich. Enjoy!