We served these with cocktails and our guest asked if we could skip dinner, and plate up another round. The mushrooms are creamed in sherry, the onions are caramelized in Marsala and then the savory layers are placed on top of charred, crusty bread and finished with shaved Parmigiano-Reggiano, thyme leaves, micro greens and a drizzle of truffle oil! WOW…
Heat a heavy-bottomed pan over high heat. Once the pan is hot, add vegetable oil. Once the oil shimmers, add the onions and salt. Do not stir immediately. Wait 1 minute, then begin to stir frequently over high heat for 5 minutes, or until the onions have released liquid and started to become translucent. Turn the heat down to medium and add Marsala. Cook, stirring often, for what will seem like an eternity, until the onions are fully melted and dark brown, approximately 20 to 30 minutes.
Heat a heavy-bottomed pan with high sides over high heat. Once the pan is hot, add vegetable oil. Once the oil shimmers, add butter. When butter foams, add mushrooms and cook, stirring occasionally, until the mushrooms have released their liquid and are golden brown, approximately 15 to 20 minutes. Reduce heat to medium low and, using a wooden spoon, create a well in the middle of the mushrooms. Add thyme, salt, black pepper and shallots; sweat until shallots have cooked through and become translucent, approximately 3 to 5 minutes. Return heat to high and add sherry vinegar to deglaze pan, then add cream and bring to a low boil. Check for seasoning. Mushrooms can be reserved until needed, then reheated over a medium flame. Add a splash of extra cream to loosen, if needed.
Grill or toast bread to a light char. Spread 2 tablespoons caramelized onions over each piece of toast, followed by approximately 1/4 cup of creamed mushrooms. Toast may be cut in half for smaller servings. Garnish with Parmigiano-Reggiano shavings, thyme leaves, micro greens and truffle oil.