Mushroom Tarts with Walnuts and Caramelized Onions make an elegant appetizer or first course. However, it also works deliciously as a casual lunch or light dinner when served with a lightly dressed salad of simple mixed greens alongside.
- 1 cup walnuts
- 2 (10-inch) puff pastry sheets
- 3 tablespoon unsalted butter
- 2 onions (peeled and cut into ½‑inch slices)
- salt and pepper (as needed)
- 3/4 pound baby bella mushrooms (or similar, stems trimmed)
- 3 tablespoon olive oil
- chopped chives (as garnish)
Preheat the oven to 375°. In a pie plate, bake the walnuts for about 8 minutes, or until lightly browned, then let cool and coarsely chop. Line a baking sheet with parchment paper, set aside.
Lay the puff pastry sheets on a lightly floured surface and cut out eight 4‑inch rounds about 1/8 inch thick. Transfer the rounds to the prepared baking sheet and prick all over with a fork. Cover with another sheet of parchment paper and set a baking sheet on top. Bake the pastry for about 25 minutes, or until it is cooked and lightly browned; remove the pastry from the oven, take off the top baking sheet and discard top piece of parchment. Set rounds aside. Increase the oven temperature to 425°.
Meanwhile, melt the butter in a large skillet set over medium-high heat. Add the onions and a pinch of salt. Cook, stirring constantly for about 4 minutes; then bring the heat to low and cook, stirring often, until golden and jammy, about 55 minutes. Set aside a few moments to cool then, using a food processor, coarsely puree the onions with the toasted walnut pieces. Season lightly with salt and pepper.
Bring a medium saucepan of water to a boil. Add mushrooms and blanch until just tender, about 2 minutes. Drain, pat dry and slice ¼ inch thick.
Spread the pastry rounds with the onion/walnut puree and arrange the mushroom slices, overlapping, on top. Choose the best looking slices as you might not use them all. Brush tops with olive oil and bake for 12 to 15 minutes, or until the edges begin to brown. Garnish with chives and serve.