Step 1

In a large skillet, add the olive oil and butter, cook over medium-high heat. Add the onions and 1/4 teaspoon each of salt and pepper. Cook, stirring every so often, until the onions begin to soften and caramelize, about about 15 minutes.

Step 2

Add the sliced mushrooms and thyme, continue cooking until the mushrooms are soft, about five minutes. Stir in the wine and cook until evaported. Remove from the heat.

Step 3

Preheat oven to 350 degrees F.

Step 4

Roll out the puff pastry sheets and cut each sheet into 9 squares (18 squares total). Place squares on a piece of wax paper or parchment paper (this will prevent sticking).

Step 5

Divide the mushroom mixture among the 18 squares, top with havarti cheese. Don't overfill or else it will be very difficult to seal edges.

Step 6

Brush egg wash around the perimeter of each pastry square and carefully fold dough over filling to create triangles, pinching edges closed to create a good seal.

Step 7

Generously brush the top of each turnover with egg wash, sprinkle with sesame seeds. Place on a parchment paper lined baking sheet.

Step 8

Bake for 15 to 20 minutes or until lightly golden. Serve immediately with a sprinkle of chopped fresh thyme and flaky sea salt.