Croissant aux Champignons

Mushroom, Gruyère & Thyme Puff Pastry

Makes: about 12 small craft-service pastries

Mushroom Filling

1 lb mushrooms, preferably a mixture of cremini, shiitake and/or oyster
1 small shallot, finely minced
1–2 cloves garlic, minced
1 Tbsp butter
1 tsp fresh thyme leaves
1 tsp Dijon mustard
¼ cup dry white wine
½ cup thick béchamel/Mornay sauce
¾ cup grated Gruyère
2 Tbsp finely grated Parmesan
Freshly ground black pepper
Salt, to taste

Pastry

1 package good-quality puff pastry, thawed but cold
1 egg + 1 Tbsp water, beaten, for egg wash
Additional Gruyère for the tops, optional

Make the Mushroom Filling

Chop the mushrooms quite finely. You want small pieces rather than slices.
Heat a large skillet over medium-high heat. Add the butter and mushrooms. Don't crowd the pan. Cook until the mushrooms release their moisture and then continue cooking until they are deeply browned and almost jammy.
Add the shallot and cook until soft and lightly caramelized.
Add garlic and thyme. Cook about 30–60 seconds, just until fragrant.
Add the Dijon and white wine. Stir and cook until the wine has completely evaporated.
Remove from the heat and let the mushrooms cool for a few minutes.
Stir in the thick béchamel/Mornay, Gruyère and Parmesan. Season with black pepper and taste for salt.

The finished filling should be thick enough to mound on a spoon. If it looks loose, cook it a little longer. You don't want moisture migrating into the pastry.

Assemble

Heat oven to 400°F. Line a baking sheet with parchment.
Cut the cold puff pastry into approximately 3½–4-inch squares or rectangles.
Put a generous spoonful of mushroom filling in the center, leaving a border around the pastry.
Fold into a triangle or rectangle and press the edges firmly to seal.
Crimp the edges with a fork if you like.
Brush with egg wash. Cut one or two tiny vents in the top.
Refrigerate the assembled pastries for 10–15 minutes before baking if the pastry has softened.
Bake at 400°F for about 18–24 minutes, until dramatically puffed and deeply golden.
Let stand for 5 minutes before serving.

Craft-Service Notes

The mushrooms are the key. Don't rush them. You want them dark, concentrated and almost dry before the sauce and cheese go in.

Make the filling the day before. Refrigerate it overnight. Cold filling is much easier to work with and gives you a better puff.

For the cheese: Gruyère is my first choice. Emmental works for a more traditional French-café character; a little Comté would be gorgeous if you have it.

For the sauce: Use a very thick béchamel/Mornay, not a pourable sauce. Your usual butter + flour + garlic + cashew milk + nutmeg approach will work beautifully here; add the Gruyère and Parmesan after thickening.

The finished pastry: flaky, deeply browned puff pastry with a hot, creamy mushroom-and-Gruyère center. This should be served warm or at least slightly warm if possible.