Preheat to 300F

In a skillet over medium heat melt butter, and pan fry mushrooms and onions until soft and cooked through. Season with salt and pepper to taste.

On each half of the baguette, evenly spread the cooked mushrooms and onion to cover the cut side of the bread.

Sprinkle with freshly grated cheddar cheese, to your liking

Toast until cheese is all nicely melted through, about 5 minutes

Drizzle with ketchup before serving and enjoy warm.