How to Make It
Preheat oven to 400ºF. In a 12-inch nonstick skillet, heat 2 Tbsp. oil over medium-high heat. Add mushrooms; cook, stirring occasionally, until they release their liquid and begin to turn golden, about 10 minutes. Add garlic and thyme; sauté for 1 minute. Season generously with salt and pepper. Add sherry; cook, stirring, until almost evaporated. Remove from heat and swirl in butter. (You can make mushrooms 1 day ahead; do not add butter. When ready to serve, reheat mushrooms in a skillet, then swirl in butter.)
While mushrooms are cooking, brush baguette slices with remaining 1 Tbsp. oil; arrange on a baking sheet. Bake until beginning to crisp, about 6 minutes. Let cool.
Spread goat cheese on toasts; top with mushroom mixture and serve.