To start with, cut the onion in half and slice. Slice the mushrooms. If they are too big, cut in half and slice.
Make Quick Caramelized Onions
Heat 1 tablespoon olive oil in a large skillet (cast iron or nonstick) over medium high heat. Add the onions and stir fry for about 2-3 minutes until translucent. Add sugar, salt and balsamic vinegar and reduce the heat to medium. Continue cooking for 5 more minutes or until softened.
Cook the Mushrooms
Add sliced mushrooms to the onions and increase the heat to medium high. Wait until they release liquid and cook, stirring occasionally, until the liquid is evaporated and mushrooms start to brown, for about 8 minutes.
Add minced garlic and 2 sprigs thyme (stems removed) or 1 teaspoon dried thyme and cook for 2 more minutes.
Toast the Baguette
Preheat the oven to 400 F or 200 C. Slice the baguette straight across if you prefer smaller crostini or on the diagonal for larger and longer crostini (see pictures) with a serrated knife about 1/2-inch thick.
Arrange them on a baking sheet. Brush with 1 tablespoon olive oil and top with vegan mozzarella shreds.
Toast in the oven for about 5 minutes or until the cheese starts to firm on top and looks golden. If you are using stale baguette, use the broiling function of your oven instead and check the cheese after 3 minutes. Remove from the oven.
Make the Balsamic Dijon Dressing
While the bread is toasting, make the balsamic mustard dressing. In a small bowl or pitcher, whisk together Maille Dijon Originale Mustard, extra virgin olive oil and balsamic vinegar.
Assemble the Crostini
Top the cheesy crostini slices with caramelized onion mushroom mixture and drizzle with the balsamic Dijon mustard dressing. Sprinkle with salt and freshly ground pepper to taste and garnish with fresh thyme. Serve warm or cold. Enjoy!
Notes
Cook’s Tips
Slice the baguette straight across if you prefer smaller bite-sized crostini or on the diagonal for larger and longer crostini with more room for toppings (see pictures).
Cut the bread about 1/2-inch thick so it doesn’t fall apart.
Add sugar and balsamic vinegar to quickly caramelize onions.
Serve them as a part of a festive appetizer table, with soups, stews, shakshukas, salads or on their own as a vegan finger food snack or a quick lunch.
Store crostini in an airtight container in the fridge for up to 3 days. Reheat in the microwave if needed.
Recipe Variations
Use any type of mushrooms or a blend for this recipe. Wild mushrooms, shiitake, chanterelles, white button mushrooms and oyster mushrooms are all great for crostini in any combination.
Substituting eggplant for half of the mushrooms will increase the nutrient density and give the crostini an interesting flavor profile.
For a non-vegan version, use shredded mozzarella or creamy cheeses like ricotta ( use this vegan ricotta recipe), chevre or cream cheese (vegan version). If you use creamy cheeses, smear toasted crostini with a thin layer of cheese.