Ingredients
Method
- Prepare the phyllo: Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper. Unroll the thawed phyllo dough and cut it in half crosswise. You will use one half for this tart.
- Layer the crust: Brush one sheet of phyllo with melted butter. Place another sheet on top, brush again, and continue layering until you have about 5-6 sheets stacked, brushing each layer with butter. Trim the edges to create a neat rectangle roughly 9x12 inches.
- Sauté the aromatics: In a large skillet over medium-low heat, melt 2 tbsp of butter. Add the diced onions and a pinch of salt. Cook for 8-10 minutes until completely soft and translucent but not browned.
- Cook the mushrooms: Increase heat to medium. Add remaining 1 tbsp butter to the skillet. Add the sliced mushrooms and cook for 5-7 minutes, stirring occasionally, until they have released their moisture and started to brown slightly. Add garlic and thyme in the last minute of cooking. Season with salt and pepper. Remove from heat.
- Assemble: Spread the mushroom mixture evenly over the phyllo layers, leaving a 1-inch border on all sides. Sprinkle the majority of the Gruyère cheese (leaving 2 tbsp aside) evenly over the mushrooms.
- Bake: Brush the exposed edges of the phyllo with the beaten egg wash to encourage browning and sealing. Bake for 15-18 minutes, or until the crust is golden brown and crisp, and the cheese is melted and bubbly.
- Cool and serve: Let the tart cool on the baking sheet for 5 minutes before slicing. This helps the layers set and prevents it from falling apart when cut. Slice into squares or triangles to serve.
Nutrition
Notes
I keep this recipe in rotation because it requires minimal active chopping but delivers maximum satisfaction. The secret lies in sweating the onions low and slow to draw out their sweetness without browning them, which balances the robust flavor of the mushrooms perfectly. It’s elegant enough for guests but forgiving enough for a Tuesday dinner when you’re tired.