Add 1 Tbsp butter, 1 tablespoon of olive oil and 1 shallot to a skillet and cook over medium heat, stirring, until translucent and golden in color, about 5-7 minutes. Tilt the skillet to one side, bring the onion to the raised top allowing the fat to gather at the bottom. Remove the onion to the same plate as the pine nuts and let cool
Slice a baguette into 1/2 inch slices. Drizzle with olive oil or spread a thin layer of room temperature butter on both sides. Place on a baking sheet and toast in a 400°F oven until golden in color, about 15-20 minutes. Flip each piece upside down halfway through for better browning (alternatively, you can brown the crostinis in a skillet. Just melt some butter in a skillet, add the baguettes slices and brown one side. Melt more butter and flip the baguettes to brown on the other side). Let cool. Top with the mushroom spread, then top with 1 slice of the sauteed mushroom.