Equipment
Ingredients
Produce
- 400 g yellow onion, thinly sliced
- 300 g cremini mushrooms, sliced
- 2 garlic, minced
- 5 g fresh thyme, leaves picked and chopped, stems discarded
Dairy & Fats
- 30 g unsalted butter
- 30 ml olive oil
- 80 ml heavy cream
- 30 g parmesan cheese, finely grated
Base & Seasoning
- 250 g rye bread, cut into 12 slices
- 15 ml balsamic vinegar
- kosher salt
- black pepper, freshly cracked
Nutrition (per serving)
Method
Using a chef's knife and cutting board, thinly slice the yellow onions and cremini mushrooms. Mince the garlic and pick the fresh thyme leaves.
Heat the butter in a large skillet over medium-low heat. Add the sliced onions and a generous pinch of kosher salt. Cook slowly, stirring occasionally with a wooden spoon, until deeply browned and caramelized. Deglaze the pan with balsamic vinegar, scraping up any browned bits, then transfer the onions to a bowl.
Wipe the skillet clean and place over medium-high heat. Add the olive oil and sliced mushrooms in an even layer. Sear without stirring for 3 minutes to develop a brown crust, then toss and continue cooking until all moisture has evaporated and the mushrooms are browned all over.
Reduce the skillet heat to medium-low. Stir the minced garlic and chopped thyme into the mushrooms, cooking for 1 minute until fragrant. Pour in the heavy cream and grated parmesan cheese. Gently simmer until the cream reduces and thickly coats the mushrooms, then season with salt and black pepper. Remove from heat.
Arrange the rye bread slices on a baking sheet. Toast in an oven preheated to 180 C / 350 F for 5 to 7 minutes until the edges are crisp but the center retains a slight chew.
Layer each toasted rye bread slice with a generous spoonful of caramelized onions. Top evenly with the warm creamy mushroom mixture. Garnish with a crack of black pepper and extra fresh thyme leaves, then serve immediately.
Chef's Notes
- Caramelizing onions requires patience. Do not rush the process by turning up the heat, as this will fry or burn them instead of slowly drawing out their natural sugars.
- When searing mushrooms, leaving them undisturbed initially is crucial. Constant stirring causes them to release their moisture too quickly, resulting in steaming rather than caramelizing.
- For a sharper flavor contrast against the rich toppings, lightly rub the toasted rye bread slices with a raw garlic clove before assembling the crostini.
- Rye bread provides an excellent, sturdy base that holds up well against moisture, but cutting the slices too thick will make the appetizer difficult to bite through. Aim for half-inch slices.
Storage
Refrigerator: 3 days — Store toppings separately from the bread in airtight containers.
