01 -
In a large skillet over medium-high heat, add the olive oil and butter. Once the butter is melted, add the mushrooms, salt, and ground black pepper. Stir to coat the mushrooms in the oil and butter mixture. Cook mushrooms for five minutes.
02 -
Add the Worcestershire sauce to the mushrooms, stir, and cook for another five minutes, or until mushrooms are a deep brown color. Once cooked, remove from skillet and transfer to a plate to cool. Select the better looking mushrooms and set them aside as reserved mushrooms, leaving behind the broken or smaller pieces.
03 -
To make the cheese spread, add the mayonnaise, sour cream, and melted butter to a bowl and whisk until combined. Next, add in the garlic, onion flakes, and black pepper. Stir those into the mixture. Finally, add the four cheeses and the green onions. Fold until evenly dispersed throughout.
04 -
Place the bread in a single layer onto a large sheet pan. Put it under the broiler until lightly browned. Remove the bread from the oven, flip the slices over, and toast the second side as well. Allow the bread to cool slightly until just warm to the touch.
05 -
Fold the cooled mushrooms (not the reserved ones) into the cheese mixture. Spread the cheese and mushroom mixture onto each toast. Top the toasts with the remaining reserved mushroom slices.
06 -
Place the sheet pan back in the oven under a 500°F broiler and carefully watch while the cheese begins to bubble and brown. Keep under the broiler until the cheeses are fully melted and you achieve your desired color, approximately 3-5 minutes.
07 -
Top with additional green onions as a garnish and serve immediately.