Heat a large skillet and melt butter.
Add mushrooms, garlic, and thyme; cook until lightly browned and tender.
Remove mushrooms and set aside.
Add shallots, salt, pepper; sauté until fragrant.
Discard garlic and thyme, add sherry vinegar and crème fraîche; simmer.
Adjust seasoning and remove from heat.
Place mushrooms on toasted bread, top with arugula.
Add poached eggs and Gruyère cheese.
