Mushroom bruschetta is such a chic and gourmet-looking offering for cocktail parties and gatherings, but it's so easy to make! Bake the crostini ahead of time and store in an air-tight container for up to a day. The assembled bruschetta can be served warm, but will hold up for about an hour at room temperature.
Heat the oven to 375°F. Slice the baguette into 24 ½” slices and spread evenly over a baking sheet. Brush each side with olive oil (about 2 tablespoons total). Sprinkle the tops with sea salt.
Transfer the baking sheet to the oven and bake until the crostini are golden brown, flipping once halfway through, 10-12 minutes. Remove from the oven and set aside until you're ready to assemble. If making the crostini in advance, allow to cool, then place into a sealed container for up to 1 day.
Heat butter and remaining two tablespoons olive oil in a 12” skillet over medium high heat until the butter melts. Add mushrooms and toss to coat in the fat. Saute, stirring occasionally, until the mushrooms have released their liquids and the edges are browned and crispy, about 15 minutes.
Add garlic and rosemary and sautee, stirring frequently, until fragrant, 2-3 minutes.
Add white wine to deglaze the plan - cook, stirring frequently, until all liquid is absorbed.
Assemble the bruschetta. Spread a teaspoon of ricotta cheese over the crostini, top with a tablespoon of sautéed mushrooms, then season with salt and pepper to taste. Serve immediately, or set out at room temperature for up to one hour.