To prepare the filling, in a large saucepan over medium heat, warm the olive oil. Add the shallots, leeks and garlic and cook, stirring occasionally, until translucent. Add the mushrooms and cook, stirring occasionally, until lightly browned. Add the wine and butter and cook, stirring occasionally, until most of the liquid has evaporated. 

Transfer the mushroom mixture to a food processor and pulse until the mixture is blended but not pureed. You want this to have some texture.

Preheat the oven to 375°F. Lightly oil a baking sheet (use more than one baking sheet if needed). 

Place the puff pastry on the prepared baking sheet. Spread the mushroom mixture evenly over the pastry. Sprinkle with the Gruyère and thyme. Bake until golden brown, about 25 minutes. Let cool, then cut into bite-size pieces.

Top each piece with a small amount of the aioli (recipe below). 

To prepare the aioli, in a food processor, combine the mayonnaise, pine nuts, garlic, lemon juice, salt and pepper and process until blended. Set aside until ready to serve.